When my grandmother holidayed in Cornwall she’d blame any gastrointestinal unease on the ‘foreign’ water. More intrepid travellers can also be disproportionately concerned about drinking water quality, yet most travellers’ tummy comes from unhygienically prepared solid foods rather than drinks. True water-borne infections are surprisingly rare, although for those who are wild camping it is worth being aware of the risks and precautions. Generally if you are far from big centres of population, the risks are small, unless you scoop water out of a brook just downstream from a dead elk. If you are concerned that drinking water might be dodgy, the best sterilisation method is to simply bring it to a good rolling boil. Such wet heat is destructive to almost all microbes, even at altitude. Anyone who is very young, old and frail or has a struggling immune system (including those travelling with cancer or within some months of treatment) might put any boiling water into a thermos. Keeping hot water hot improves sterility, and this can be used to make up baby food or breakfast porridge.
Brewing up isn’t always practicable so people can either ask for boiling water in a cafĂ©, or use water sterilising tablets. Different kinds are said to have differing efficacies but assuming you use the cleanest source of water available, it probably isn’t crucial what chemical you choose. If your source is muddy, gritty or highly contaminated, sieve it through cloth before adding a purification chemical, and allow plenty of time (usually 30 mins) for it to do its work.
Lots of travellers are persuaded to spend on water sterilisation devices but personally I’m less enthusiastic about using water filters since they can get lost or broken, and a little pot of water purification tablets takes up much less room. Iodine is probably the most effective of the choices although the newest chlorine-based products are also great purifiers. Due to European Union regulations iodine can no longer be sold in the EU to purify water, although tincture of iodine is still available and can be used, even if you need to take care not to allow it to spill and dye your undies. Add four drops of tincture of iodine (usually 2%) or use 3% Lugols iodine to one litre of water. Shake well and leave to stand for at least 20 mins. If the water is very cold (e.g. glacial melt water) or it is cloudy, double the iodine concentration or leave the water to stand for longer – hours if possible. The taste can be neutralised AFTER purification by adding vitamin C powder or tablets.
The photo below shows a traditional hand pump which generally dispenses safe water.