Water Purification

The World Health Organisation estimates that globally some 2 million people a year die from water borne diseases.  It is recommended that all wild water should be considered as potentially contaminated and should therefore by subject to one of the subsequent treatments described here. 

When travelling always remember the just because the endemic population drink the water doesn’t mean it’s safe for you to drink. Some degree of immunity will be gained by the local population through repeated exposure and you will have no idea how many will go on to have health problems directly attributed to the water.  It is still common practice in mountain areas even in the UK for hikers etc. to fill up there water bottles from mountain streams.  This is simply playing Russian Roulette and statistically if you do this often enough you will eventually succumb.

There are generally considered to be 5 main classes of contaminants that can occur in water and we will look at these in order of size starting with largest.  These are termed particulates. This includes all the general bits and pieces that can end up in water like bits of organic matter such as grass, leaves, twig, dead insects, etc. etc. and also non organic matter such as sand and silt.  Most of these things are all visible to the naked eye ranging from several millimetres across down to the smallest sand particles which can be 60 microns across (0.06 mm) for comparison a human hair is 100 microns thick.  Silt is generally considered to be less than 60 microns.

In general most of these particulates won’t actually do you any harm (although the silt in glacial run off can irritate the digestive tract) but they can harbour some of the other classes of contaminants and thus reduce the effectiveness of some of the purification techniques.  It is recommended, therefore, that these particulates should be removed by filtering before some of the purification methods such as chemical, boiling or UV are used.  Filtering is easily achieved by simply passing the water through densely woven fabric. Millbank bags made of tightly woven canvas were issued to the armed forces up until recent years and can still be obtained, but it is easy to improvise with clothing.  Clean sand also makes a passible filter.

The next group of pathogens in order of size is parasites. This includes a range of creatures from parasitic worms; tapeworm, roundworm, hookworms, etc., flukes, and single celled protozoa of which Giardia and Cryptosporidium are the most notorious.  Most of these parasites have several stages to their life cycle and spend part of the life in other animals before their eggs or cysts end up in the water to be ingested by us.  Depending on the organism they can produce a variety of symptoms from the very mild to death in extreme examples.  Giardia is becoming an increasing problem globally and is spreading with human travel.  It is a particularly difficult parasite to treat in water, especially with chemicals and is one of the main reasons why filtration needs to take place before purification.

Next down in size are bacteria. These include a range of bacteria that enter the water from faecal contamination such as E.coli, C.diff, Dysentery, Salmonella etc. plus things like Leptospirosis which is transmitted through rodent urine.  Again they can produce a range of symptoms but  sickness and diarrhoea is common. Leptospirosis can cause Weils Disease, which can be fatal.

Next down are viruses.  These include hepatitis A, polio, norvirus etc.  Viruses tend to be quite fragile and are easily dealt with by most purification methods.

Finally the smallest contaminants found in water are chemicals. These can include heavy metals form industry. Nitrates, organo-phosphates from agricultural runoff, blue-green algae toxins, etc. etc.  These are the hardest group to deal with as many of the traditional purification techniques will not remove chemicals.  The best solution is to reduce and minimise the likelihood of chemicals being in the water by always sourcing cleanest water possible i.e. upstream from heavily farmed areas, industrial areas etc.

The method of purification will often be dictated by circumstances.  When you have the facilities to boil this is often the simplest way.  Always filter first for the reasons described but with the exception of a few species of bacteria which rarely occur in water and chemicals, boiling will destroy pretty much everything.  By holding water at 100⁰C for one minute most bacteria, and all parasites and viruses will be destroyed, even the difficult to remove Giardia and Cryptosporidium.  We recommend that to make sure that all parts of the water get to are held at boiling point for enough time, bring the water to a rolling boil and boil for 4 minutes. It’s probably over the top but why take the risk?  Always boil in a pot with a lid or kettle to minimise evaporation which could concentrate chemicals if they are present.

There are many other ways to purify water.  Chemicals, including iodine (now banned in the EU), chlorine, silver, potassium permanganate etc. all have their draw backs.  The ones most commonly used are (were) Iodine and chlorine which are quite reactive chemicals and should not be taken for extended periods or in high doses (often necessary if Giardia is suspected). They are both denatured by UV light and need time to work. And they taste horrible.

Other method include UV pens, MIOX (mixed oxidants) pens.  As with boiling and chemicals it is necessary to filter the water first and both these methods rely on being able to obtain batteries for them to work.

The finally brings us on to pump style filter/purifiers.  There are many different makes on the market coming in all shapes and sizes and utilising different methods of purification.  Before investing in such a device ensure that it both filters and purifies.  Check that it removes protozoa, bacteria and viruses (some will even remove chemicals).  Check the method of purification; ones using iodine or chlorine are likely to still leave a taste in the water. Check how long it takes to pump a litre of water and how many litres it will pump before it needs replacing or maintaining.  With that done you pay your money and take you choice.  But always consider at what cost your health. It doesn’t always pay to go with the cheapest.