How to Purify Water

How to purify water, Water purification, Purify water, Water camping

Often we go camping and simply can’t carry enough water for our whole trip so resort to using river water. But to drink this without treating it to remove waterborne nasties would be cavalier and will put you at risk. Read on to find out how you can purify water and save your back from carrying  a few kilos.

Why should I purify water?

The main dangers of drinking unpurified river water come from bacteria (salmonella, E.coli, shigella, for example), viruses (hepatitis A virus) and parasites (giardia lamblia, entamoeba histolytica). In the tropics you can add typhoid and cholera to the list. Water can be exposed to acid rain, storm water runoff, pesticide runoff, and industrial waste.

If you have been drinking river water and start suffering from vomiting, diarrhoea, fever, unexplained rashes, jaundice, or any other illness, you should go and seek urgent medical help. Let your doctor know where you have been and what you have been doing. That said there are a number of simple water purification techniques you can use to ensure you won’t get ill.

When it comes to water purification whilst camping, carefully choose where you draw your water from.  Don’t take it from sluggish water or stagnant pools. Avoid gathering from areas where there are signs that animals have been present. It’s worth walking at least fifty metres up stream to check there aren’t any nasty surprises like dead animals, sewage, and animal dung. Choose water that doesn’t have too much sediment.

If camping near a river make sure that you designate a toilet area well away from your water source. You should be clear to everyone that they must bury their waste 15cm deep and ideally at least 30 metres away from the river. Obviously practicing good personal hygiene such as washing hands with bio-degradable soap (normal soap can damage the eco system of a river) before handling food, eating, and after using the toilet helps to keep you safe.

Once collected, there are a number of water purification methods which are described below.


Boiling, is the oldest means of purifying your own water. If the water is cloudy, filter it through clean cloths or allow it to settle, and draw off the clear water for boiling. Water should be brought to a rolling boil for no less than 1 minute. If you’re worried about conserving fuel, the same results can be obtained by bringing water to a boil and then turning off the stove but keeping the container covered for several minutes. In general leaving water covered whilst it cools is best practice and it gives you an extra margin of safety.At altitudes greater than 2000 meters (6,562 feet), water purification needs a 3 minute boil time. This may be the easiest and most effective method but of course it will use up valuable fuel.

Boiling is not necessary to kill common intestinal pathogens, but it is the only easily recognisable point that doesn’t require a thermometer. All organisms except bacterial spores, which are not usually waterborne enteric pathogens, are killed in seconds at boiling temperature. Therefore, any water that’s boiled for 1 minute  (allowing for a margin of safety) should be adequately disinfected.

However there are downsides to boiling water, firstly it does not improve the taste, smell or appearance unlike for example a filtration unit. You also need to be aware that boiling water can be re-contaminated once you store it so make sure whatever storage container you use is clean.


How to purify water, Water purification, Purify water, Water camping

UV Light

Ultraviolet Light can be used to combat some microorganisms. The technology requires the water to be nice and clear so if it is cloudy you will need to pre-filter it.  The correct power delivery, and correct contact times to achieve maximum pathogen reduction are essential as is reading the manufacturer’s instructions.

Effective against all pathogens: bacteria, viruses, and protozoa. UV treatments do not actually kill pathogens, they simply prevent the organisms from reproducing. UV systems also benefit from normally being very light weight.

Downsides are that it doesn’t strain out particulate unless of course you have pre-filtered your water. It won’t affect the taste of the water (could be good/bad). UV also doesn’t have any last decontaminating properties so you must ensure your storage container is clean. UV might be an effective method in pathogen reduction in backcountry water but there’s a lack of independent testing data available on specific systems.

Sun light

If you find yourself in an emergency situation you can disinfect water by using sunlight but there are caveats. Pour the water into a clear plastic bottle and ideally stand it on a reflective surface such as tin foil or inside your mess tin. If the water stands in bright sunlight for a minimum of six hours it will be safer to drink but this technique will only work if the water is clear. Cloudy water stops the sun light from being effective. However this is a technique to only be relied upon in an emergency!


Filtering eliminates bacteria and Cryptosporidium, but not viruses. A variety of filters are available from camping stores. Most have filter sizes between 0.1 and 0.4 microns, which will remove bacteria from water. Microns are a measurement of the pore size of the filter. The smaller the pore size the more nasties it can filter. The smallest bacteria is about 0.2 microns but a filter of 0.1 microns is recommended by the Centre for Disease Control and Prevention.

There are problems with filters as they cannot remove viruses. However there are technologies coming onto the market to combat this utilising hollow fibres and reverse osmosis. Filtration systems are larger and heavier than all of the other water treatment processes which is a major consideration if you are heading off for an extended hike.

The best advice is to use a combination of filtration and chlorine dioxide as this has a very high effectiveness at removing Combination filtration and disinfection has a very high effectiveness in removing and killing Giardia, Cryptosporidium, bacteria and viruses.  when used with chlorine dioxide and an absolute less than or equal to 1 micron filter (NSF Standard 53 or 58 rated “cyst reduction / removal” filter).


There are a variety of chlorine and silver based tablets available on the market today. When used correctly they destroy most bacteria but are less effective for viruses and cysts such as hepatitis A virus, giardia and amoebic cysts, cryptosporidium.

We would not use chlorine alone as it can be inactivated, tastes rancid, and its action changes with different water pH.

Chlorine dioxide

Chlorine dioxide is a much more effective water treatment than chlorine. As above you need to read the pack instructions, ensure that the treatment bottles are in date, and only use the measurements and treatment times the manufacturers stipulate. It’s highly effective in killing Giardia, viruses, and bacteria but only has a low to moderate effectiveness against Cryptosporidium.

How to purify water, Water purification, Purify water, Water camping

Chlorine dioxide does not prevent re-contamination of your water so you must ensure that the water bottle you store it in is clean.

Once the water is clean you can buy some neutralising tablets to mask the taste of treated water but they don’t neutralise it completely. We have used chlorine dioxide alone and can confirm that it is palatable. Chlorine dioxide treatments like the Life Systems drops are the lightest and smallest water treatment method.


Iodine has historically been an effective method for purifying water but is now seldom used. In fact it is no longer recommended and it is banned from use in EU countries.

There are multiple downsides to using Iodine. Its efficacy decreases with lower water temperatures and decreasing water clarity. It’s not effective in killing Cryptosporidium. This microscopic parasite causes the diarrheal disease cryptosporidiosis. Iodine is also only low to moderately effective at killing Giardia.

Iodine is not recommended if you are pregnant or have thyroid problems of for those with known hypersensitivity to iodine, or for continuous use for more than a few weeks at a time. It’s also corrosive and can stain your clothes.

Finally of course any water treated with iodine will taste pretty merciless although you can neutralise this taste.

How to purify water, Water purification, Purify water, Water camping,


When treating water there are many variables you need to be aware of such as contact time, treatment concentration, water temperature, water turbidity (cloudiness), water pH, the concentration of disinfectant. Depending on these factors, 100% effectiveness may not be achieved.

We use chlorine dioxide and boiling as our main method of water treatment. Whatever your source of water is, be sure to keep your water collection system clean and maintain it well.

There is always a risk when drinking river water but the above treatments help to lower this risk.

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