FAQ - Drinking Water Safety

This page is a work in progress. Comments and commercial information is welcome.
Send to the maintainer Roger Caffin


Outdoor activities carry their own risks of injury and death. Neither the Confederation nor the maintainer nor any other contributors to the FAQ pages have any control over what the reader does, and cannot accept any liability for any loss or accidents which the reader might suffer. The contents of this web site must NOT be relied upon for technical advice. Failing all else, read the NSW Civil Liability Act 2002. If you don't know what you are doing, get competent advice from your doctor.


Once upon a time, long long ago, you could drink from a mountain stream and be confident you were getting better water than they serve up in the towns and cities. But not any more: you stand some chance today of getting a nasty bug or wog, and too many of us know this only too well. Why is this so, and what has gone wrong? Sadly, there are now several dangers lurking in our watercourses which can harm you. There are also lots of other things there which won't. Telling these apart and knowing what to do means we have to start by understanding the enemy.

That said, we should add that it is not necessary to be hyper-paranoid. If you are in an area where you know the water comes from a pristine catchment, it is probably not necessary to do anything other than make sure the water looks clean and clear. But if the river has passed through a farmed or built-up area, watch out! The author doesn't bother with treating the water from most of Wollemi National Park or from the side-streams leading out of Kanangra into the Coxs River, but usually treats the Coxs River itself (just for example) with a filter. Whites River in Kosciusko NP is a known Giardia hazard, what with all the novices staying in Whites River Hut etc.

Some places in the bush are claimed to have 'bad water'. Curiously, these places seem to be popular with young novice walkers and youth groups, and it is usually members of these groups who get sick at these places. Just how one spot on a river can have 'bad water' while the rest of the river doesn't is a mystery. Hopefully these kids will eventually learn to wash their hands after going to the toilet.

In addition there are now two other pressures: a pre-occupation with 'hydration' and with 'hydration' equipment. The former is a recent 'drink till you gurgle' fad (which can kill), and the latter is a straight Marketing effort. The main target with these products is your wallet.


What's Reasonably Available For Use?


The 'Hydration' Fad

A recent but dangerous fad concerns how much water you should drink each hour. This subject has caused considerable debate on aus.bushwalking, and considerable debate in the medical arena as well it seems. The vendors of 'hydration bladders' would like us to all buy their products; the vendors of sports drinks and/or electrolyte replacement drinks would also like us to part with our money - in their direction. 'Hydration' has become a buzz-word in the last 20 or so years, with a corresponding surge in the sale of bottled water. Curiously enough, most older bushwalkers manage to get through some pretty long hard walks without indulging in any of this forced drinking exercise. So what is the truth of all this?

The author of this FAQ is prepared to give his (only slightly biased) opinion that it is all crap: a combination of raving bandwagon by people with no knowledge of medical facts mixed with the opportunistic urgings of vested interests. That's right: there is not a single bit of genuine medical research to justify the 'hydration craze'. What research there is seems to highlight the hazards of excess water - see for example the Invited Review by Valtin in the American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 2002. This hydration myth has even reached that debunker of Urban Myths, Snopes.com, which opines:

The exhortation that we all need to satisfy an arbitrarily rigid rule about how much water we must drink every day was aptly skewered in a letter by a Los Angeles Times reader:
"Although not trained in medicine or nutrition, I intuitively knew that the advice to drink eight glasses of water per day was nonsense. The advice fully meets three important criteria for being an American health urban legend: excess, public virtue, and the search for a cheap 'magic bullet'."

Should you wish further information on this, see the FAQ section on Water, Salt, Cramps, Electrolytes and Sports Drinks, especially the section on Hyponatraemia. We repeat: people have died from following the hydration craze and drinking too much water while exercising.


What's in Water?

As usual, we start with theory. It's not that hard. Broadly speaking, there are four main classes of contaminants:

Each category requires different handling to meet the requirements of the American Environmental Protection Authority (EPA). This organisation is the largest internationally-recognised certification body for water purifiers. Having dealt with the theory, we then move on to explain the differences between the categories of filter, purifier and so on. Finally, when you have understood all of that, we list some commercial units, and make a few recommendations. Sure, it's technical, but so is gastro.

Dissolved materials

This category covers 'natural' things and is relatively harmless, assuming you exclude the third category. Tannic acid is the stuff which leaches out of timber and makes some streams brown - especially in Tassie. Just warm this up, add milk and sugar, and behold: tea (or coffee)! Apart from dissolving any natural fibre clothing and rotting the guts out of leather boots, it will do you no harm. However, too much of this sort of stuff can make the water difficult to treat.

Ordinary salty or brackish water will do you no harm either, although it may not be very useful for survival. Anyhow, these things don't rate for this FAQ.

Suspended matter

In general this stuff won't do you much harm either. Much of it can be filtered out with a handkerchief if you are worried by the appearance. We bailed and filtered water out of a muddy soak once: despite filtration through cloth it remained the colour of milky tea. It stank too: it was stagnant. But it did us no harm. The one exception is blue-green algae: it is very toxic so leave this stuff well alone. How to tell whether something is blue-green algae is not covered here: I don't know.


This category is different from the first one by definition. It includes all the sorts of industrial and agricultural chemicals which can do you a nasty. To be sure, normally you would not expect to meet many of them in the bush, but you can. Downstream from intensive agriculture and orchards is one danger zone, sadly. And being downstream from some mines is another hazard: the Tonalli river near Yeranderrie carries arsenic from the old silver mines. Charming. (Side note: the NPWS was happy to absorb the area into the Park, but less happy when they realised that it was now the NPWS rather than the previous owners who had to bear the cost of the compulsory remediation!)

Water with any of these chemicals in it cannot be treated very reliably. Activated carbon is supposed to take many chemical out, but there is no guarantee, and how do you know when your filter has exhausted its cleaning capacity? For your safety, seek better water elsewhere. Don't use water draining from any of these areas.

'Bugs and Wogs'

Now we are getting serious. This category is the one to worry about and the one this FAQ is mainly about. It includes several sub-categories of nasties, arranged by size:


These are extremely small, generally well below 0.1 um in size, down to 0.004um. They include the rotaviruses which come with various dangers, the polio virus, and many others. Not all are lethal: the common cold is a rhinovirus. In general you will not be in too much danger from viruses in the bush, which is fortunate as most filters cannot reliably filter them out of the water: they are much too small.

However, beware when downstream of any Sewerage Treatment Plant! We were on the Nattai River below Mittagong some years ago and drank the water after careful filtration through a Katadyn filter. The virus load from the STP went through the filter. We got home that day, but spent the next 24 hours on our backs in a very bad way. This was a worry as the Nattai goes straight into the Sydney water supply, which is one reason it has to be treated so heavily. The ironic part is that, since the Mittagong Council refused to clean up their STP, or couldn't afford to (and didn't need to for their rate-payers), the State governemnt was forced to fund a new plant for them. It's called politics.

Some filter manufacturers (eg Katadyn) claim that viruses are always attached to something larger and so can be filtered out. Well, this may work for 99% of the viruses in the water, but 1% is still quite enough to make you very seriously ill. One filter manufacturer (General Ecology) claims that their patented filter can remove viruses by an extra process: this appears to be accepted by the EPA. See under Filters for more information.

While not a serious concern in Australia, viruses are a real hazard when you go overseas, especially to places like Nepal and Africa. There are several reliable solutions: boil the water, treat it with iodine or chlorine dioxide, or use a UV steriliser. Chlorine will treat many viruses, but has serious weaknesses on other bugs; other chemicals are very suspect. We will return to these treatments later.


These generally fall in the 0.4 to 1um range. They include things like cholera, salmonella, legionnaires and of course Escherichia coli. To a biologist and others of that ilk, they are a different sort of beastie to a virus. In fact, it is possible for a bacterium to carry a virus inside it.

For bushwalkers the big risk is the E coli bacterium. It is commonly used as a measure of faecal contamination, which gives you a very good idea of where it comes from. In your bowels it is fairly harmless, and almost everyone would have them there. However, if it gets into your stomach it will cause big problems: diarrhoea and dysentry, not to mention a 'crook gut'. It cannot go backwards from your bowels to your stomach: it has to get there down your throat. What is a bit more of a worry is that there are several variations or strains of E coli, including one which can be fatal.

Some very popular camping sites have an undeserved reputation for having 'bad water'. I am willing to bet that much of this reputation derives entirely from the number of young inexperienced campers who have got sick there, and that in all cases it was really because they didn't wash their hands after going to the toilet. That much said, some of the creeks in the Blue Mts had a very bad reputation because of the appalling sewerage management practices the towns there used to have. Fortunately this is being cleaned up now - again by the State Government. However, it is known that cows do carry some strains of E coli which can be quite dangerous (or fatal) to humans, so watch out.

There are three practical ways of dealing with bacteria. You can boil the water, filter the water with a good rated filter, or treat the water with a chemical.


This category includes the Cryptosporidium family and the now well-known Giardia lamblia. Protozoa are large, typically over 6 um in size. Cryptosporidium seem to be widespread at a low level, even in Sydney's water pipes, while Giardia are spreading across Australia. Originally we did not have Giardia in Australia, but trekkers or returning Australians have brought them in and now we are stuck with them. I gather the Giardia cysts are spread by the likes of foxes and possibly some native animals, but they originally come from humans. G lamblia is probably the major hazard for walkers. Under a microscope, an active G lambia looks a bit like a mad face (see line drawings), not that this helps you much. As a cyst (left hand line drawing) it looks like a very small egg, in a hard case.

They have a complex life cycle: after you swallow them they hatch out of their cysts in your stomach and attach themselves to the walls of your bowels (guts?). If you look at the middle line drawing you will see what looks like a huge sucker on the right hand side at the bottom: it is. Then they grow there, feeding off your blood stream by sucking blood through the walls via that sucker, and then they turn into several cysts (ie they multiply) and pass out of you (in the usual way). If they get a chance they will float around in water until some other being drinks the water, then they wake up in the gut and start again. Every 12 hours they fission or divide into two. This may not sound like much, but after ten days of infection you could have a million of them growing there on your blood supply and irritating the hell out of your bowels.

The symptoms of a G lamblia infection develop slowly, taking a week and a half to two weeks to become apparent. If you feel sick the day after drinking suspect water you can be reasonably sure it is not G lamblia. In general, you won't notice any symptoms until well after you have got home from the trip. If you are infected you become sensitive to any fats and rumble very loudly, usually in public. You can be infected for weeks before you wake up to the fact that something is the matter, and in that time you will be spreading a huge load of cysts for others to ingest. It seems that some people get really hung up on the whole Giardia thing: there is even a Giardia Club in America! Reality check: they sell water filters and chemicals for outdoors people. But the site has lots of good information.

The big worry is that it isn't just humans who carry G lamblia: quite a few other animal populations can spread it around, including foxes and some native animals. The Whites River corridor in the Snowy Mts, beloved of skiers in winter, is notorious for it. Personally, I put much of the blame on the pit toilet at Whites River Hut: it was so dilapidated that most people were not game to step on the floor, let alone sit on the seat, for fear it would collapse under their weight. You can work out the rest for yourself. However, the NPWS has recently replaced this toilet, so we will see if there is any improvement in that valley.

Even so, this means that there is G lamblia right across the Snowy Mts now, and likely to stay there. The same applies to many (most) other mountain areas including the Blue Mts. Assume the water you are about to use is contaminated.

There are several practical ways of dealing with protozoa. You can boil the water, filter the water with a good rated filter, treat the water with a powerful oxidising chemical or treat it with UV light. Note especially that research papers report that chlorine and some other chemicals will not work reliably on G lamblia, no matter what the vendors claim on their packets, and it seems that even iodine is not always entirely successful against Crypto. Their hard cyst shells are a great defence. However, it seems that both UV light and chlorine dioxide are effective.

Nematodes and larger

These are even bigger, and can be as nasty as any of the above or worse. They are not that common in Australia, and can be filtered out quite easily. You will run into them overseas in the tropical and Asian areas. Some, quite delightfully, bore into your skin (through your feet for instance), enter your blood supply, and take up residence in an internal organ. Very charming. Ultimately I believe some of them can be fatal.



In practical terms in Australia you need to avoid chemical contamination and be able to treat water for E coli and G lamblia. There are many ways of treating water for these bugs, which we list here in general terms.

Along the way, note that the term 'purification' is controlled by the EPA in America and means there should be no active bugs left in the water, and is quite different from the term 'filtration'. Water which has been 'filtered' may legally contain anything, as explained above.

Industrial methods of purification include osmotic filtration, UV irradiation, treatment with ozone, treatment with chlorine dioxide and other ways needing heavy engineering. Industrial methods are not covered here, although I know one company was trying many years ago to promote hydrogen peroxide solution. However, since creating this page and relegating UV treatment to the 'impractical' category, I have found a company which markets a miniature UV lamp for treating water in the bush. Another company has started to market an electrical system. Both are covered below.


This works - provided you boil the water for long enough. Some bugs are killed by bringing the water up to 70C, well below boiling, but some people claim you need to boil for at least 10 minutes. The author is not an expert on this, but suspects the 10 minutes bit is simply a precautionary overkill which has acquired legendary status. Research literature usually states that bringing the water to the boil will kill both E coli and G lamblia.

One point to watch with boiling is altitude. At 4000m the boiling point of water is depressed, so a little bit more time might be well advised. The major problems with this method are time, fuel and cooling the water down.


This is an attractive option, but requires considerable care to implement. Bacteria are very small, so you need a very fine filter to trap them. This means that you will need a lot of pressure to force the water through; it also means the filter will be very prone to blocking up with any fine dust or clay in the water. To be effective the filter should have pore sizes around 0.3 um or less. Further on we will go into more detail and list some filters which the author has tried out in surveys. Please note that the opinions expressed on these filters are those of the author but that no guarantees are given or implied (and so on). Some filters include an activated carbon core to remove bad tastes and chemical. The carbon may do so, but I just would not rely on it for nasty agricultural chemicals.

You may come across the term 'microfiltration' in this area. It is used by some vendors of bushwalking filters to describe their products. The vendors cannot describe their products as meeting the EPA requirements for water purification (with one exception) because they can't filter out viruses. Instead the vendors have informally coined this term to describe a filter which filters out enough bacteria and protozoa to meet the EPA requirements for those bugs. In fact it has no legal meaning. On this note, you should be a bit cautious about reading too much into the vendor advertising. The package the Katadyn Hiker filter comes in has (or had) a large gold sticker on it proclaiming that it met the EPA purification requirements for bacteria and protozoa. Well, it does too, but nowhere was there any mention that it did not meet the EPA requirements for viruses. Personally, I found this American advertising to be misleading.

UV Light

It is possible to sterilise water with Ultra Violet (UV) radiation. This is sometimes done commercially, with huge UV germicidal lamps. You might think (as I did) that it would not be possible to make such a thing portable for bushwalkers, but in fact it has been done by two different American companies: AquaStar and Hydro-Photon. Each of them has packaged up a miniature switch-mode power supply with the same miniature Philips germicidal UV lamp. Each company has EPA registration as a amker of UV devices (as far as I know) but they do not have EPA 'approval' for the devices themselves as the EPA does not issue approvals for this sort of product. I imagine that the lack of control over just how the user will use the device may have something to do with this.

However, while the EPA does not 'approve' such devices, they certainly do approve the UV treatment process. It is effective against viruses, bacteria and protozoa, and some other biological agents as well. Obviously it isn't going to do much for dirt or simnple chemicals, and too much suspended matter may block the UV from working very well. You can read the formal EPA Guidance document (a lengthy PDF) on UV treatment yourself.

The AquaStar device is fitted to the cap of a Nalgene bottle, which is rather clever. You get an approved treatment container plus a form of protection for the device all together. The Hydro-Photon devices are called SteriPEN, and there are now two models: the older Classic (230 g or 8 oz) and the newer and lighter (110 g or 4 oz) Adventurer.

Using one of these is fairly easy: you put water in bottle (a one-litre Nalgene say) and irradiate it with the magic wand for about a minute - until the timing light goes out. It certainly helps if the water is fairly clear. Some tests were done by some climbers in America and are being reported on the BackpackGearTest web site, and a brief mildly scientific report is available at the climbers' website.

The author has some knowledge of the SteriPEN devices, having reviewed the newer Adventurer for Backpacking Light. The Classic was a bit heavy on batteries, using four of the widely available AA cells (and it was a bit heavy anyhow). The newer and lighter Adventurer seems more frugal on power but requires two CR123 batteries. These are lighter but dearer. We eagerly await the arrival of the next generation based on UV LEDs: that will be really effective for both weight and battery life! However, it has yet to happen. Both units can take lithium and metal hydride cells, and can also take rechargable cells. For the Adventurer the company sells a matching solar recharger case to carry on the back of your pack - cute, but heavy. I am told it was originally designed for missionaries!

There are two drawbacks to the use of a UV device. The first is that you are dependent on batteries. Well, spare batteries are lighter than a spare filter cartridge I guess. The second is the shape of the discharge lamp itself. It will fit in a wide-mouth bottle just fine, but it does not really fit into the narrow neck of the PET mineral water bottles I normally use. This makes for some complications - for me.

The units each contain a little microprocessor which runs the lamp, measures the water temperature, times the dose and checks that the lamp is underwater all the time. The plastic used for water bottles is opaque to the UV light used, and the air/water interface at the top blocks the UV from hitting you as well. No, the blue glow you see in the photo is NOT UV radiation! As to the details of how it works, I have included a couple of small quotes from Steri-Pen:

Ultraviolet light disinfects rapidly without the use of heat or chemicals. Ultraviolet treatment is often used in the final stage treatment of bottled water. Operating rooms, isolation areas and other medical facilities make extensive use of ultraviolet germicidal lamps to maintain a low bacterial count in the surrounding air

Ultraviolet light treatment is a proven and accepted method for disinfecting drinking water. Short wavelength ultraviolet light, commonly referred to as UV-C occurs between the wave lengths of 200 and 265 nanometers, and this is where the most effective germicidal action occurs. The Hydro-Photon lamp produces 90% of its light at the 254.7 nanometers and is, therefore very effective as a anti-microbiological agent.

Microorganisms encompass a wide variety of unique structures and can be grouped into five basic groups: bacteria, virus, fungi, protozoa, and algae. A microorganism is composed of the cell-wall, cytoplasmic membrane and the cell's genetic material, nucleic acid. It is this genetic material or DNA that is affected by the Ultraviolet light. As UV-C penetrates through the cell wall, it causes molecular rearrangement of the microorganism's DNA, thus preventing reproduction. If a cell can not reproduce, it is considered to be microbiologically dead. Due to individual cell makeup, different levels of UV energy are required for destruction. The effectiveness of UV microbial destruction is a product of both time and intensity. The intensity of UV-C light is measured in micro-watts per square centimeter and the time is measured in seconds. Hence the amount of ultraviolet light necessary to kill a particular microorganism is reported in units of micro-watt seconds per square centimeter; this is known as the dose. UV light testing has shown that Steri-Pen provides between 38,000 and 60,000 micro-watt seconds per square centimeter. The following table shows the dose required to kill common microorganisms.

Microorganism Destruction Levels

(Ultraviolet energy at 253.7nm wavelength required for 99.9% destruction of various microorganism - in uwsec/cm2

Bacillus anthracis (anthrax) 8,700 Shigella dysentariae (dysentery) 4,200
Corynebacterium diphtheriae6,500 Shigella flexneri (dysentery) 3,400
Dysentary bacilli (diarrhea) 4,200 Staphylococcus epidermidis 5,800
Escherichia coli (diarrhea) 7,000 Streptococcus faecaelis 10,000
Legionella pneumophilia 3,800 Vibro commo (cholera) 6,500
Mycobacterium tuberculosis (TB) 10,000 Pseudomonas aeruginosa 3,900
Salmonella (food poisoning) 10,000 Influenza (viruses) 6,600
Salmonella paratyphi (enteric fever) 6,100 Poliovirus (poliomyelitis) 7,000
Salmonella typhosa (typhoid fever) 7,000 Hepatitis 8,000

Germicidal UV light - between 240 nm and 290 nm, acts on thymine, one of the four base nuceleotides in DNA. When a germicidal UV photon is absorbed by a thymine molecule that is adjacent to another thymine within the DNA strand, a covalent bond or dymer between the [thymine] molecules is formed. This thymine dymer prevents enzymes from 'reading' the DNA and replicating. Without the ability to replicat the microbe cannot reproduce and is rendered harmless.

While you are unlikely to meet many of the above bugs running wild in the Australian bush, I should point out that downstream of a sewerage treatment plant or below a pump-out area anything is possible. Overseas - who knows? We saw people collecting water from what looked a very nice little trickle by a track. Only 50 metres up the hill and initially out of sight there was a farm, outdoor toilets and a cow yard. Where had the water come from? In some places, anything is possible. No, this wasn't in Asia; it was in France!

Electrical - 'Pool Salt'

Swimming pools do get full of algae, and owners don't like that, so there is a ready market for ways of killing the algae. The most common is 'pool-chlor': a chemical (usually sodium hypochlorite) which usually stinks of chlorine. This method not only kills algae, but also most other bugs and wogs. The action is explained below. Some bleaches are similar. Neither is really suitable for drinking water. The other way of keeping your pool clean is chemically similar, but you start with ordinary salt (sodium chloride) and convert that into the powerful oxidisers using electricity. This typically uses a box of electronics which supplies several amps at several volts for a typical swimming pool. However, the author is not sure which oxidant is created: hypochlorous acid or oxygen radicals. It appears that it may create both. You would not think this could be turned into a portable method of sterilising water, but, incredibably, the Americans appear to have done just that!

The device is the 'MIOX Disinfection Pen'. It seems to have been developed by the MIOX Coorporation, but the press release I read mixed up MIOX, MSR and Cascade Designs. Cascade owns MSR, but MIOX is or was separate. One assumes a marketing arrangement. Anyhow, it looks a bit like a colourful MagLite torch and they claim it will be released late in 2003. (Late 2003: reported to be on sale in America; 2004: on sale in Australia.) The web site says:

The device operates by converting a brine solution to a mixed-oxidant solution via electrolysis. Each Purifier utilizes two 3V lithium camera batteries, a salt pellet and a tiny electrolytic cell. The Purifier will treat approximately 50 liters of water on one salt pellet and 200 liters of water on one set of batteries. The Purifier can be used over and over, making water treatment an inexpensive procedure after the initial purchase. An important feature of using simple salt as the disinfectant source is that salt has an infinite shelf life, so the Purifier will still function even if stored without use for a long period of time. The disinfectant will inactivate a number of common pathogens, including E. coli, Giardia, and Cryptosporidium, as well as chemical and biological warfare agents. The Purifier has passed the EPA Purifier Protocol, achieving more than 10 times the level of disinfection than required for normal waters.

In operation the unit is used to create a small quantity of concentrated chlorine dioxide solution which is then poured into your water bottle and allowed to ... kill all the bugs. A bit like stirring the sugar in your cup of coffee? Test strips are included to verify that you have done it properly. They are claiming EPA certification as a full purifier, which is rather nice. They claim 200 litres of water from one set of batteries plus any sort of salt you have. Better carry spare batteries and a pinch of salt!

It seems that MIOX also supply industrial-size versions to the airlines and similar units to the US military. A press release from Sept-2003 went as follows: "Mountain Safety Research (MSR), a developer of essential gear for challenging environments, today announced that the Office of Naval Research (ONR) has placed an order for 1,000 MSR(R) MIOX(R) Purifiers for the U.S. Marines. This purchase by the ONR will join that of the Office of the Secretary of Defense (OSD), which has received an order for an additional 7,000 purifiers to ensure that U.S. troops have the most cutting-edge portable water purification technology available." In addition, it handles some nasties as well: "The Purifier successfully destroyed the nerve agent Soman (GD) as well as the blister agent Lewisite (L). A 99% removal of Soman was achieved after 78 minutes, and Soman concentrations went to non-detect levels (less than 4 micrograms/liter) in 150 minutes. The mixed-oxidant solution removed Lewisite (L) to below detection in 30 minutes or less. Another chemical warfare agent, V-Agent (VX) was removed by approximately 99% in 130 minutes; virtually total removal of VX (less than 23 micrograms/liter) was achieved in 250 minutes." Hum, interesting ...


Chemical inactivation

There are several products sold for water treatment, but many of them do not work for bushwalkers facing the bugs listed above. In general they rely on one of several chemicals:

I have also seen potassium permanganate (Condy's Crystals) used in Nepal. I was assured at the time that it was iodine, but they didn't know what they were talking about because it's chemical behaviour was a dead giveaway. At the concentrations they were using, it was not very effective against much, and certainly not against the bugs and wogs we are concerned about here. It just looked good. Watch out for this one!

There is a hazard with the use of any chemical treatment. If the water is full of organic matter the chemical may be absorbed into that matter and may not manage to kill all the bugs. For this reason chemical treatment should only be used on clear or filtered water.


Let it be admitted up front: the chief disadvantage of iodine for most people is the faint hospital smell it has. With tablets it is only a smell, with little or no taste. If you don't believe me, try drinking some water which has been correctly treated with a pentavalent iodine tablet (eg Coghlans) while keeping your nose carefully blocked. You won't taste a thing. In other cases based on the resin there may be a bit of a taste, suggesting an excess of iodine in the water. For some people with thyroid problems, iodine is not suitable.

Iodine in the best form (pentavalent iodine) and correctly used generally works quickly and reliably in the bush on most bugs. That seems to be the verdict of a stack of research papers I have read by known research scientists from very credible organisations (see some references at the end of this page). There have been reports that iodine is less effective on Cryptosporidium protozoa than on Giardia, and this is a concern. The iodine may create some iodine compounds, which mean that prolonged use is not a good idea. However, Giardia is the most common protozoa and is usually killed by pentavalent iodine.

There are several ways of buying or using iodine. The simplest is iodine solution or tincture of iodine bought from a pharmacist. This is ordinary iodine crystals in a saturated solution. One version uses alcohol to dissolve the iodine, while the other uses water (eg PolarPure). You simply add a few drops of this to each litre of water. Alternately you can use a commercial iodine solution normally used for other things, such as Betadine. However, I do not recommend this method: it is not all that reliable (the oxidising power of this form of iodine is low) and you get a fair bit of smell and some taste. To be honest, I have not used it much either - for those reasons.

Several vendors market systems based on a pentavalent iodine resin. This was apparently developed by Lambert and Fina at Kansas State Uni in America for NASA (pity the astronauts), and has been licensed out by them. The iodine is in a more highly ionised form here and has far higher oxidising power. The advantage is that it certainly works on most bugs; the disadvantage is that the dosage varies with the resin approach. At the start an excess of iodine is inserted into the water because the resin is fresh. The resin remains effective for a long time, down to the stage where you can no longer taste the iodine (as long as the smell remains).

The most useful iodine treatment in my opinion uses the pentavalent iodine in a controlled quantity per litre. This way you get sufficient iodine to kill most bugs, but not an excess. This is done with tablets of glycerine hydroperiodide. I've seen two brands of tablets so far: Coghlans and Potable Aqua, but the bottles and tablets appear identical and I strongly suspect they are made by the same chemical company (it figures). It is curious that I have not seen any other brands around. You add one tablet to a litre of water and wait about 10 minutes at normal temperatures, but allow 20 minutes when it's very cold (like melting snow). Instructions usually come with the tablets. The chemical reason for preferring this form of iodine over solutions is given below.

There are health warnings attached to iodine: 'pregant women should consult their doctor', and you should not use it continuously, and so on. Iodine in high concentrations does have some effect on your body: this is known from observing people in areas where the water has very high concentrations. But - those people have lived quite happily there (apart from getting goitre) for hundreds of years, and the concentrations and amounts they get are way beyond what we would get. Limited use seems safe.

Caution: this is not medical advice: consult your doctor ...


This is the chemical used by some water authorities to kill viruses and some other bugs after mechanical filtration. It can be used in two forms: chlorine gas or as a chemical. Of recent years the water authorities have been forced to use such a high dose of chlorine that the taste of the water becomes completely yuk: to counter this they add ammonia as well. The water still tastes yuk. (We collect our own rainwater.) By the way, do not ever add ordinary tap water to a fish tank: the chlorine and ammonia concentrations may (will!) harm or kill the fish. Sydney lost a huge fraction of all aquarium fish once when things went really wrong at the treatment plant. Chlorine is used in swimming pools as sodium hypochlorite or 'Pool Chlor', and that stuff stinks of chlorine.

For portable water purification there are several commercial forms such as sodium dichloroisocyanurate (NaDCC) tablets and sodium hypochlorite solution. Both are meant to be 'stabilised' so they don't decompose into cholrine at once. In this case the stuff does not make actual chlorine gas but hypochlorous acid, which can give free chlorine in contact with suitable bugs. Free chlorine is reasonably effective against viruses and most bacteria when used in sufficient concentration. 'Sufficient' may or may not mean the water tastes yuk. However, many researchers claim that chlorine is not sufficiently effective against protozoa such as G lamblia, and it is not effective against Cryptosporidium at some stages of its life cycle. The reason is the hard case around the cyst: it blocks the action of the chlorine. Of course, if you use enough chlorine and leave the water for long enough (4 hours), it may work - but the water may have a chlorine taste.

Katadyn sell 'Drinkwell Chlorine' liquid (sodium hypochlorite), but they supplement it with an antichlorine liquid (sodium thiosulphate) for those cases where you want to drink the water. One might reasonably infer from this that it leaves a bit of a taste.

Katadyn also sell Micropur Forte MT1: a mix of silver and calcium hypochlorite. It comes in both liquid and tablet form. The reason for the silver is given below. The chlorine part is meant to kill bugs, but it takes 30 minutes before viruses and bacteria are killed by this treatment, and Giardia takes over 2 hours. Clearly, the effectiveness of this treatment is not as high as iodine.

Puritabs used to be quite common: they contained sodium dichloroisocyanurate (NaDCC). However, the manufacturer has stopped making these, and the commercial rights have been transferred to another company which is selling Aquatabs. These are, I am told, identical. The manufacturer claims they leave no taste, but the contact time for killing Giardia is very long, and it is not always effective against Crypto. On the other hand, it is supposed to be quite effective against viruses and bacteria.


This chemical is marketed for the 'treatment' of water in two forms: straight silver and mixed with chlorine. Let's make one thing very clear right at the start: silver does not kill protozoa at all, and does not kill bacteria with any speed. What silver does is inhibit the multiplication of bacteria. The vendors (Katadyn) claim the bacteria will eventually die, but I have yet to see independant verification of that. So if the water you are about to drink contains a dangerous dose of E coli, treating it with silver will not give you much protection. The silver treatment is intended for water storage tanks on boats and so on, to stop any bacteria from multiplying in the tank. As far as I know, it does a good job of this. Of course, it has no effect on protozoa like Giardia. Why do walking shops continue to sell it? An effective marketing campaign I suppose.

Chlorine dioxide

This is a new treatment in the bushwalking area, marketed by McNett Corp (USA) under the name Aquamira and by Advance Chemicals under the name Pristine (Canada). The difference between 'chlorine' and 'chlorine dioxide' is significant: the gas chlorine 'chlorinates' the bugs, and can create nasty chlorine compounds, while chlorine dioxide breaks down in a 2-step process into a highly reactive atomic oxygen, which oxidises the bugs. The method has been used by municipal water authorities to treat water for a long time, often in preference to simple chlorine. The chemical is recognised and approved by the EPA for this (with EPA registration number 70060-7-71766 I am told). However, whether the Aquamira or Pristine treatments themselves have EPA approval is another matter: my latest information is that they do not yet (2006). This is strange, and worries me. Again, I suspect it is the lack of control over the user's actions which are the problem.

The detailed chemistry is interesting (imho). Your high school chemistry will leave you thinking that chlorine dioxide shouldn't exist. It isn't all that stable, since the chlorine is in the +4 ionised state (Cl++++) rather than its more common -1 state (Cl-). Despite that, there are many ways of making it, and we have cribbed a page from one of the major suppliers in case you are interested. (Actually, this web site has a lot of information about chlorine dioxide as it is a major industrial chemical for the water industry.) I have no idea which of the listed processes is used by Aquamira or Pristine, although we do know they use phosphoric acid as the activator in part B. Anyhow, when ClO2 breaks down it first creates ionised chlorine dioxide, then it creates ionised oxygen atoms (so to speak). These are very energetic and will attack many things, in particular the sulphur atoms in basic organic matter and certain key amino acids. Cell walls are disrupted and bugs die. That's all bugs, even crypto, which iodine handles poorly. This chemical does not generate active chlorine like bleach: the chlorine ends up as a harmless chloride ion the same as you would get from salt. This means there is no chlorine taste or smell (well, very little, they say). The effectiveness looks very good on the figures I have seen so far: good enough to really 'purify' water to EPA requirements. What's more, I gather chlorine dioxide can be used on a continuing basis, unlike iodine: some towns use it for the community water supply.

What you get in Aquamira or Pristine is a stabilised form of chlorine dioxide (probably sodium chlorite with some added stabilising chemicals?) in bottle A and an activator which is fairly harmless food grade phosphoric acid (as used in Coca Cola) in bottle B. You mix 7 drops of part A with 7 drops of part B, wait 5 minutes for the brew to get going (it goes green/yellow), then tip the lot in a litre of water and wait 15-30 minutes. It was reviewed in the American Backpacker magazine in Sep 2000, at which stage McNett were applying for EPA certification. My understanding (2004) is that it is the company International Dioxide Inc which actually makes the chemicals and bottles them for both McNett and Advance Chemicals which is applying.

Are the two brands the same? A quote from Dr Ryan Jordan on BGT:

My immediate impression upon viewing the product was its EXACT resemblance to Aquamira, a chlorine dioxide treatment chemical kit distributed by the McNett Corporation in Bellingham, Washington. And by exact, I am referring to the chemical compositions and bottle shapes/sizes. Seemed like too much of a coincidence, since I knew that neither McNett nor Advanced Chemicals Inc. (Pristine's distributor) were primary manufacturers of chlorine dioxide.

So I did some checking around using the EPA registration numbers on the products as guidance (don't freak, this is all public record). It turns out that when McNett initially begain distributing Aquamira, they purchased the chemicals from the Engelhard Corporation out of Iselin, NJ. Eventually this company sold their chlorine dioxide division to a DuPont subsidiary, International Dioxcide Inc., in fall of '99. And it turns out, lo and behold, that International Dioxcide Inc. is the supplier of chlorine dioxide to Advanced Chemicals Inc. for use in their Pristine product. But it still is not clear whether the small bottles of Aquamira or Pristine have EPA approval themselves.

The point of this is not to provide interesting history, because it's really not. It's just to emphasize that there is probably no functional difference between Pristine and Aquamira, and their effectiveness shouldn't be markedly different. How effective they are is another matter.

Chlorine dioxide safety

Is chlorine dioxide safe and effective? The EPA has this to say about it. It would seems so, as long as it is in solution. The gas form is another matter, but we would not encounter that. However two special cases can cause problems. The first is chlorinated tap water, curiously enough. It seems that the extra chlorine in the water can react with the chlorite ions or the chlorine dioxide and liberate chlorine gas. This smells and is bad for your nose and mouth. Hint: it is no use testing Aquamira out on chlorinated tap water! The second case is water with a high level of sulphur in it. This is not all that common, but can happen. The sulphur can be oxidised to sulphur dioxide, which can form sulphuric acid. Testers have reported quite an acid burning sensation when this happens. However, I believe sulphur-laden water would normally smell rather badly, so you should be able to pick that case out. Few walkers in Australia would encounter this.

Hydrogen peroxide

This treatment is so new it hasn't reached commercial form yet. The idea is similar to the chlorine dioxide one: create free ionised oxygen atoms. In fact, 'peroxide' has been used to bleach hair for a long time: it is the same effect. It has also been used as the oxidising part of a rocket fuel. It suffers from the same problem as chlorine dioxide: it is not very stable, so how you cart it around safely has not been worked out. Doin't hold your breath waiting.


Chemical action

Just how do these chemicals work? We can illustrate this using the well-known Pool-Chlor example. When chlorine gas dissolves in water the molecule breaks into two atoms or ions. One becomes a chloride ion, the same as you get by dissolving common salt in the water. This chloride ion has little or no effect on bugs: salt is not a disinfectant per se. The other chlorine ion reacts with a molecule of water to form hypochlorous acid - similar to the sodium hypochlorite in 'Pool-Chlor'. This is an oxidising agent of some strength. It reacts with the organic molecles in the wall of the bacterium, and causes the cell to break down. (Chemically, a redox reaction.) There is a similar action on viruses. So far, so good. Unfortunately, the chlorine does react with many organic materials to created chlorinated compounds, and these can be nasty.

However, cysts such as G lamblia have a hard outer egg-shell (in effect). This shell is sufficiently thick and stable that the hypochlorous ion does not cause enough damage quickly enough. The shell is resistant. A stronger oxidising agent is needed. The pentavalent iodine ion is a sufficiently strong oxidiser that it can penetrate and damage the shells of many cysts. The pentavalent iodine ion has a very high electron deficiency in its outer shell, and attacks with greater power. That is why it is so much more effective than ordinary dissolved iodine, and can be used at a much lower concentration. However, it does create some iodised compounds, and people with thyroid problems are sensitive to iodine.

Going on from there, we have the ionised oxygen from chlorine dioxide. This is even more powerful, and targets particular parts of bugs. It will kills Crypto, Giardia, bacteria and viruses, very effectively. What's more, the left-overs are harmless, and the water tastes 'fresh' (or so many testers claim).

A rather interesting resource for information about chemical disinfection is the American EPA web site. However, they are primarily concerned about municipal supplies, so finding the information there is a bit difficult. They do have a whole pdf book on chemicals which can be downloaded, chapter by chapter. The Chapter 4 is on chlorine dioxide for instance.


Post-treatment treatments

The trouble with many of the chemical treatments is that they leave a taste or smell in the water. Some people don't like that, although I don't mind a faint whiff of iodine (not a strong taste!) as that reassures me that the water has been treated and is safe. So most vendors offer ways of reducing this taste or smell.

It is possible to use activated carbon to remove most chemicals from the water after treatment, and Vitamin C tablets can remove the iodine and sodium thiosulphate can remove chlorine. However, I strongly recommend you do NOT do this. Leaving the very small amount of chemical in the water means the water stays bug-free. It is only too easy to contaminate the water again by using a dirty cup or something.

In fact, several purifiers were withdrawn under EPA orders from the market not too long ago because the activated carbon post-filters which were parts of the systems turned out to be too effective at removing the chemical too quickly. The chemical was not staying in the water long enough to kill all the bugs. Exactly how this came to light I am not sure, but it was a worry!

In short, post-treatment treatments are a bad idea and should not be used.


EPA Certification

Much is made of the Environmental Protection Authority (EPA) registration some manufacturers proclaim. In fact, there is some confusion here. I am slowly working it out for myself, so what follows is my 'best guess' so far. Any substance put in drinking water to kill pests (or bugs) in America must pass EPA safety rules (and be registered) as a pesticide, and this includes chlorine, iodine, silver and so on. (Well, logical I suppose: a pesticide kills pests!) A quote from the EPA web site says:

Antimicrobial Pesticides

Antimicrobial pesticides are substances used to control harmful microorganisms including bacteria, viruses and fungi on inanimate objects and surfaces primarily in indoor environments. Types of antimicrobial products have traditionally included sanitizers, disinfectants, and sterilants.

A "sanitizer" is a substance that significantly reduces the bacterial population in the inanimate environment, but does not destroy or eliminate all bacteria or other microorganisms.

A "disinfectant" is a substance that destroys or eliminates a specific species of infectious or other public health microorganism, but not necessarily bacterial spores, in the inanimate environment.

A "sterilant" is a substance that destroys or eliminates all forms of microbial life in the inanimate environment, including all forms of vegetative bacteria, bacterial spores, fungi, fungal spores, and viruses.

EPA's Registration of Pesticides

Before a pesticide can be marketed and used in the United States, EPA must evaluate the pesticide to ensure that it meets federal safety standards. EPA grants a registration (or a license) for a public health pesticide product only after the Agency has reviewed efficacy and safety data to ensure that, when used according to the specific instructions on the label, the product is effective and does not cause any unreasonable adverse effects on human health or the environment. Such evaluation is particularly important for antimicrobial pesticides (sanitizers, disinfectants, and sterilants) which are used to reduce or eliminate microbial contamination.

The pesticide label provides specific safety precautions and use directions for handling or using the product. EPA has concluded that pentavalent iodine and chlorine dioxide products registered to date have met federal standards for environmental and human health safety.

But being registered as a pesticide apparently does not necessarily mean the treatments actually work as a 'purifier'. The EPA also has a certification system for means of 'purifying' water, and this means reducing all bugs - viruses, bacteria and protozoa, by a certain amount.The amounts are shown below, and this is where we play an amusing game called "nines". Those of you familiar with quality control will have met this before. Basically, the treatment is assessed as removing 99.9% (3 nines), 99.99% (4 nines), or 99.9999% (6 nines) of the incoming bugs, as shown below.

Reduction required for Viruses Bacteria Protozoa
a Purifier 99.99% 99.9999% 99.9%

Of course, when you are claiming to have removed 99.9999% of incoming bugs, there is a problem of proving it. If there are one million bugs in a litre of water coming in, you should not let more than 1 bug through. Bacteria for instance may be of the order of 1 micrometre in diameter: how do you count just 1 of them in the litre of water? As well, how do you make sure the litre of water being tested does not get contaminated after filtration: 1 bug in a litre is not a lot. So we also have testing thresholds: a level below which the testing laboratory cannot detect the bugs. Tricky. It is usually necessary for manufacturers to have their products tested at several laboratories, just to get some cross-checks. Don't worry too much about this: just check for EPA certification.


'Microfilters' - so called

Now, where things get complicated is in the area of microfilters. It turns out there is no EPA certification for a 'microfilter'! (I thought there was, along with many other people. I was wrong.) Many companies in the filter industry have agreed among themselves that products should meet the bacteria and protozoa sections of the EPA requirements to qualify as a 'microfilter', but not the virus part. That is, 'many companies', but not all, and there is no legal significance here. Some companies choose to play by a different set of rules - which they define themselves.

The very small size of bacteria means the filter must block everything down to about 0.3 micrometres. The simplest solution would be to have a membrane with holes of 0.3 micrometres or smaller. However, life is never that simple: how do you do this? The normal filter is actually a sort of dense matrix or mesh like a sponge, with holes of various sizes, and works in a maze-like manner. So two figures are usually quoted: an average blocking figure and an "absolute" blocking figure, with the latter being the higher of course. What this means is that particles blocked do not stay on the surface: they usually are embedded below the surface and getting rid of them is difficult. For many filters the only recourse is to replace the filter cartridge (at a cost); a few can have the surface cleaned. However, some filters rely on more than just mechanical blocking, and are thereby more effective. More on this later.



The laws on advertising in America are different from those in Australia. It is possible to advertise something in America with words which, while technically correct, might lead you to believe that a product has been certified by the EPA as a 'purifier'. That is, the marketing might boldly claim that the product meets EPA purifier requirements for bacteria and protozoa, while remaining quite silent on the fact that it does not meet the EPA requirements for viruses. A well-known and popular filter has this on the packaging. The author's personal opinion is that this could be misleading for someone who does not know enough to realise the difference.

Finally, some words of warning. There are lots of kitchen filters on the market. They may improve the flavour of water by taking out the chlorine flavour of the suburban water supply, but many of them are of little or no value to bushwalkers. In general, they are a plug of activated carbon. Forget them. There are also a number of genuine filters made for household and outdoor use. Some are too heavy, being made for car-based touring or major expeditions with lots of porters, but there are light ones made for bushwalkers. On the other hand, there are some filters which the author regards as being a bit 'dodgy' - or maybe it is the companies promoting them which rate as 'dodgy'. Naming these here could incur all sorts of legal hassles, so we won't. But if the company's claims seems just a little hyped (and they aren't listed here): you have been warned. We will simply note that several companies have been successfully prosecuted in America for deceiving the public. Finally, you may see references on web sites to home-made filters using a plug of cotton wool in a container placed in-line to a hydration bag. I am sure these take out the big lumps, but those wouldn't hurt you anyhow. I am equally sure I would not rely on any of them for genuine nasties. The advocates are fooling themselves.

Filters and Filter Life

If you are going to rely on a filter, you need to be sure it will keep working. There is no absolute figure for the volume of water you can put through any filter. It all depends on how much stuff there is in the water. If you try filtering cloudy water, you can kill the filter with just a few litres (been there, done that). The clay particles which make the water cloudy are very effective at blocking any filter. What happens is you find that the force required to work the filter goes way up. Then you have to replace the filter core or cartridge, or in some cases clean it.

Caution: just because the creek water looks clear does not mean there isn't a whole of of suspended matter in it. Often there is. Very fine particles of mica are a real trap: there can be a whole lot of it in the water while the water looks quite clear. You look at the lovely creek, see all the stones at the bottom, and think you will filter straight from the creek. Big mistake: this can wreck a filter in one day.

There are three ways of improving filter life: settling, pre-filtering and surface area. Each is good: all three are better. We always collect our water in a water bucket and let it stand for a little while before filtering. That lets a lot of the larger suspended matter settle out, especially stuff like mica and silt. Don't be tempted to skip this step.

If you use a pre-filter you can block an awful lot of the finer rubbish before it gets to the critical filter surface, but the pre-filter will need replacing or cleaning often of course. Some vendors use a fine sponge as a pre-filter: easy enough to clean but fairly coarse. Other vendors sell quite fine pre-filters: you might like to check these. Some walkers stick a coffee filter paper or similar over the inlet tube: very cheap, very light and fairly effective too. Some walkers filter the water through a couple of handkerchiefs first, but that usually means things really are a bit difficult! However, if there is a lot of organic matter floating around this can be very effective. Cleaning the handkerchief afterwards may be dificult though.

The third way of increasing the filter life is to copy air filters in cars and use a larger surface area. Most bushwalking filters units have a filter core or cartridge which is a smooth cylinder: the surface area is small. The Hiker filter (originally sold by Pur, until Katadyn bought Pur from Proctor & Gamble) uses a cartridge which looks just like an air filter: a huge surface area pleated down to a small volume. The vendor was so confident about the extended life of this design they used to give a 12 month guarantee on the cartridge. This is a bit meaningless if you try to filter cloudy water, but we do normally get this sort of life out of a cartridge despite very heavy use. More recently they just guarantee a volume of water going through. This unit seems to be the most common one we have seen around the world. I own two hiker filters, and have done both an Owner Review and a Field Test Review of them. Both were very favorable.


Most filters use an inlet hose, a pump, a filter body housing the actual filter cartridge, and an outlet hose. This is convenient and allows you to fill various containers. However, there are variations. We must emphasise here that if you put the (potentially contaminated) inlet hose on the outlet by mistake, you could have a problem. For safest results, keep them separated, and flush the outlet hose just in case each time you use the pump. Katadyn refuse to supply an outlet hose for this reason on their ceramic models, but I found that made life a bit too awkward.



Some 'filters' include a chemical treatment core, and therefore are effective against almost anything. In principle this turns them into a 'purifier', and made them very good for overseas travel in places like Nepal and Africa. The technical difference between 'filter' and 'purifier' was explained above. However, some of these units also had a carbon post-filter to remove the smell of the iodine immediately, and this turned out to be not such a good idea. The carbon post-filter was too effective: it stripped the iodine out of the water before it had enough time to kill all the bugs. As a result some of these units had their EPA purification certification withdrawn. They still work as "filters", but are not 'purifiers'. I asked Pur about this and received the following reply:

"Procter and Gamble stopped selling PUR purifiers in June 2000 - they are currently not available. A quality control test indicated that the PUR Voyageur did not remove 99.99% of viruses in every condition when the StopTop carbon cartridge was used. The test did indicate full effectiveness against protozoa and bacteria."

It may be better to use a straight filter and then treat the water afterwards with iodine. This is very reliable. One filter, the First Need, has certification as a purifier but gets it without chemicals. How they do this is quite interesting, and is covered below.

Sports Bottles

There are a number of filters and purifiers shaped like sports bottles, with a drinking tube at the top. This is fine for drinking, but it has two disadvantages. The first is the small capacity of these units: not so good when you want a couple of litres of water for dinner. The second concerns the units which have an iodine core: the short transit time between core and mouth means that either the bugs are still alive when they go down your throat, or the concentration of iodine has to be very high. I have little experience with these, but I am not enthused by the idea. They seem to cater to the American yuppie 'now, now, now' impatience.



These must provide substantially bug-free water under EPA rules: they must remove or deactivate protozoa, bacteria and viruses. Adequate boiling, iodine or chlorine dioxide treatment and osmotic filtration can do this, but most ordinary filters can not (with one exception). In Australia purification is not normally needed, but in places like Nepal or Africa it is essential. If Crypto (protozoa) is a known problem chlorine is ineffective and the iodine may be unreliable.

So in general if you need to cope with viruses you will need to use chemical treatment. To get the best results the water should be fairly clean to start with, otherwise most of the chemical used may get absorbed by other organic matter and will not get to attack the bugs. Many vendors use a combination of surface filter and iodine core, and this works very well. Some vendors made the mistake of offering a carbon post-filter to remove smell of the iodine they usually used in the core. As mentioned above, this didn't work out, and these units do not appear be available any more. However, I would personally be happy to use one without the post filter as long as I could still get that whiff of iodine from the water afterwards. That whiff is one guarantee of safety.

The General Ecology First Need filter/purifier has a different sort of filter element and holds EPA certification as a purifier, without using chemicals. This is achieved by some very cunning chemistry on the surface of the filter element or matrix. The filter itself is rated to 0.1 microns or 0.4 microns absolute. This is larger than viruses, but apparently they tend to be charged, so the manufacturer makes the filter surface charged with the opposite polarity, so it attracts and catches the bugs. I have read some of the literature and research papers, and I am moderately impressed. At the same time, the opposition points out that the technology is sensitive to both changes in the acidity of the water and the level of organic mater present. If you go from limestone country to a peat bog you will get a severe change in acidity (pH), and this may release all the captured viruses held in the matrix. This can happen in Australia. In addition, many peat bogs have quite high levels of tannic acid and other humic or organic matter present, and this stuff may clog the charged surface up so it no longer attracts. However, these comments come from the opposition, while the Furst Need unit does have current EPA certification, so it is hard to tell how much is just normal sour grapes. I was lent a unit for field trial courtesy of the importers, and I have put up a bit of a comparison with the Hiker.


Overseas use and paranoia

If you are going overseas it makes double sense to be very careful about your drinking water. The dangers of the water in various exotic locations are well known, with all sorts of names for the local form of diarrhoea. There are two reasons for this hazard. The first is that some areas are just dangerous. The second is that while you may have no trouble at home, you will have little immunity to the local flavour of bugs overseas.

In some countries it is sufficient to take the same precautions as you would take at home. We used a Hiker for six weeks in France and had no problems. The local walkers never bothered. Fortunately, the cartridge lasted the distance (we were careful), because buying a replacement outside of a really major city was impossible.

If you are really paranoid about water but don't like iodine, one good solution is to combine a filter with a tasteless chemical. Filter the water with a reasonable filter to get rid of the protozoa and bacteria, then treat the filtered water with a chlorine or oxygen treatment to kill any viruses. Several vendors recommend this approach, selling both the filter and the chemical. If you do this you do not need to filter down to 0.2 um: a unit filtering to 0.3 um or even coarser would be fine. Another approach would be to use the First Need purifier, since this takes out the lot. However, if you are going for a long trip you will need to consider taking spare cartridge(s) with you. They are rarely available in the field, and relying completely on them leaves you just a little exposed. Mind you, the same applies to other combinations. Finally, you could use one of the chlorine dioxide treatments: they seem suitable for continued use and do 'purify'.



Once again, since there are so many choices available the majority of walkers will disagree with most of the recommendations given here, and certainly some vendors will, so I have got to be wrong. Regardless, I will make a few.


Available Filters

This information may be out of date: if vendors wish me to update it they should contact me: I will be happy to listen. Purifiers and chemicals follow. Web sites for the products are listed in the Brands section. Walkers should remember that buying spare cartridges can be difficult out of major cities and in some countries.

Available Purifiers

This information may also be out of date: if vendors wish to update it they should contact me. I will be happy to listen.

Available UV systems

This information may also be out of date: if vendors wish to update it they should contact me. I will be happy to listen.

Available Chemicals

This information may also be out of date: if vendors wish to update it they should contact me. I will be happy to listen.


References, for light entertainment

"Giardia, An emerging issue in water management", Proc, Apr-89, ANU
"Animal reservoirs and cross species transmission of Giardia", Davies & Hibler, Waterborne transmission of Giardiasis, Ed Janbowski & Hoff, 1979
"Effect of resin disinfectants I3 and I5 on Giardia muris and Giardia lamblia", Marchin, Fina, lambert & Fina, Appl & Env Microbiology, Nov 83
"Giardiasis", Juranek, CDC, (memo, publication unknown)
"Back country water treatment to prevent Giardiasis", Ongerth et al, Am J Public Health, Dec 89
"Effect of chlorine on Giardia lamblia cyst viability", Jarroll et al, Appl & Env Microbiology, Feb 1981
EPA document on UV systems, found at http://www.epa.gov/safewater/disinfection/lt2/pdfs/guide_lt2_uvguidance_draft.pdf

© Roger Caffin 1/3/2002