Water Treatment Options

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 eff


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  that it would not be possible to make such a thing portable for bushwalkers,

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.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.

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.

The author has some knowledge of the SteriPEN devices, having reviewed the newer Adventurer. 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.

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.

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, we 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!

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:

  • Iodine
  • Chlorine
  • Silver
  • Chlorine Dioxide
  • Hydrogen peroxide

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.

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