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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.
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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.
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.
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.
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.
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.
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.
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 diphtheriae 6,500 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!
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 ...
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.
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
Are the two brands the same? A quote from Dr Ryan Jordan on BGT: