Water Purification

Introduction
Boiling
Halogens
Filtration
Sources of Equipment

Introduction

Travellers may find themselves exposed to the organisms that can cause travellers' diarrhoea. Enterotoxigenic E. coli, Shigella, Entamoeba histolytica, Salmonella, Campylobacter, Giardia, Cryptosporidia, Cyclospora and rarely Vibrio cholerae are spread through the faecal/oral route.

In areas where it is difficult to maintain hygiene and sanitation, travellers are advised to take food and water precautions including water purification. Where water needs to be purified prior to drinking, then it should also be purified for e.g. brushing teeth. Even where bottled water is readily available, it is usually a good idea to have a back up system for purification should bottled water run out. In addition, purification is generally agreed to be more 'environmentally friendly' than bottled water since the same bottle can be refilled with purified water.

There are several different methods of water purification, some are more effective than others. The decision on which method to use should take into consideration the likely level of contamination of water at the destination and also whatever is deemed most practical and acceptable to the traveller.

The main methods of water purification are:

Boiling
Halogens
Filtration.

Boiling

This is the most reliable method, although stoves, kettles and heating coils may be inconvenient to use while travelling. Although varying time periods are quoted, for all practical purposes, boiling for one minute is sufficient to kill all harmful organisms. This applies even at higher altitudes when water boils at a lower temperature. It is generally accepted that bringing to a rolling boil achieves adequate purification.

This may be the most acceptable method for travellers going to visit friends and relatives where access to equipment is possible. Water purified in this way should be cooled and covered to avoid contamination after boiling.

Halogens

Halogens are cheap and easy to use and may be the method of choice for those on the move such as backpackers and expeditioners.

Chlorine and silver

Chlorine and silver based tablets are available from chemists and specialised travel equipment shops. When used correctly they destroy most bacteria (e.g. Vibrio cholerae), but are less effective for viruses and cysts (e.g. hepatitis A virus, giardia and amoebic cysts, cryptosporidium).

Chlorine alone is readily inactivated by organic matter and its action varies with pH. However if used in combination with phosphoric acid in combination (e.g. Aquamira) it is more effective and this combination will destroy both giardia and cryptosporidium.

Chlorine Dioxide

Chlorine dioxide is available in tablet or droplet form and is cheap, safe and effective. Chlorine dioxide will kill bacteria, viruses and cysts in water (including giardia and cryptosporidium). Follow directions in the pack for effective use.

Iodine (no longer recommended)

For many years this was the recommended method of chemical water purification for travellers. However, new EU directives (Oct 2009) have banned iodine for this use and it is no longer available in EU countries for the purpose of water purification.

Filtration

Filtration is useful for those who may only have access to brackish water such as rivers and streams, as filters remove particulate matter.

A wide variety of filters are available. Some versions have cores which can be replaced. Filters remove sand, clay and other matter as well as organisms by means of small pore size, membranes, adsorption, exchange resins and osmosis. They effectively remove bacteria and parasites but not viruses. Good filters are effective against cryptosporidium and giardia. Due to the inability to remove viruses, filtered water must also be chemically treated or boiled.

Filtration combined with chemicals

Some modern filters incorporate a method of chemical disinfection to increase their effectiveness. Such filters should be replaced after a specified volume of water has been treated, although this could sometimes be difficult to keep track of.

Sources of Equipment

Outdoor and adventure holiday shops and pharmacists

Equipment for sterilising water and water filters can usually be purchased at outdoor sports, camping and adventure shops. Chlorine preparations can often be obtained from local pharmacies. Filters for sterilising water must not be confused with cheaper versions (sometimes available in supermarkets) designed only to remove smells and chlorine from domestic water.