Water can contain not only visible debris and harmful microorganisms, but also chemical pollutants. Water should only be drunk if its purity is known. This also applies to water used for making ice cubes and cleaning teeth.
In areas where it is difficult to maintain hygiene and sanitation, travellers are advised to take food and water precautions, that includes water purification. In these areas water should only be drunk if it is bottled (with an intact seal), boiled, chemically disinfected or passed through a reliable filter. 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:
This is the most reliable method of removing microorganisms, but will not remove debris. A rolling boil for one minute achieves adequate purification. Water should be boiled for 3 minutes at altitudes above 2000 m (6562 ft) where water boils at a lower temperature.
Water purified in this way should be cooled and covered to avoid contamination after boiling.
If water is not boiled, a combination of techniques to disinfect water should be used, and can include the use of filters (ceramic, carbon, membrane), chemical disinfectants/halogens and/or UV radiation.
Filtration traps and removes debris and microorganisms from water. Filtration is useful for those who may only have access to brackish water such as rivers and streams, as filters remove debris. Filter pore size largely determines how effective a device will be, although micro-organisms will also stick to the filter material. Filter pore sizes between 0.1-0.4 µm are usually effective at removing bacteria and parasites but may not adequately remove viruses.
If this type of filter is used, filtered water must also be chemically treated or boiled.
A wide variety of filters are available and prices vary accordingly.
Manufacturers’ literature should always be checked prior to use.
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 can be difficult to keep track of.
Chlorine Dioxide is available in tablet or droplet form and is cheap and effective (e.g. Aquamira). Chlorine Dioxide will kill bacteria, viruses and some parasite cysts in water. Follow directions on the pack for effective use. It is ineffective against the parasite Cyclospora.
Halogens are cheap and easy to use and may be the method of choice for those on the move such as backpackers and expeditioners. Halogens are readily inactivated by organic debris, which should be removed first. They inactivate bacteria and viruses but not parasite cysts. The main halogens used are:
Chlorine, (usually as Sodium or Calcium hypochlorite) is the most commonly used disinfectant in municipal water supplies worldwide and is non-toxic.
- Iodine (no longer recommended)
Since Oct 2009, EU directives have banned iodine for this use due to toxicity concerns. It is no longer available in EU countries for the purpose of water purification.
Ultraviolet (UV) light can destroy bacteria viruses and some parasite cysts. The effectiveness of this means of water purification depends on the UV dose and exposure time used. This method requires that the water being treated is clear as the effectiveness of the device may be limited in water that is very cloudy or has a high level of debris in it. Battery-operated pen devices that deliver a metered, timed dose of UV are available and may be an effective means of disinfecting small amounts of clear water.
A hand-held device works by passing a small electrical charge is passed through a solution (using the device) generating the production of oxidants, including hypochlorite. This solution is then added to untreated water and according to the manufacturers inactivates bacteria, viruses and some parasites. It is unlikely to be effective against the parasite Cyclospora.
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. The manufacturers leaflet should be consulted prior to use to ensure the product eliminates all pathogens that you may be at risk from. 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 odour and chlorine from domestic water.
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