Eating and drinking: Water purification

The safest source of drinking water is invariably the bottled variety, particularly in developing countries. But if you're in a remote spot where it's impossible to buy water, there are three ways to make water drinkable. Always cover water once it has been treated.

Boiling

Water should be kept at a full boil for at least five minutes to rid it of bacteria and other harmful micro-organisms. Vary boiling times according to how dirty your water supply is and your altitude - water boils at lower temperatures the higher up you go.

• Heating coils with a plug and adaptor are useful if you don't have access to a kettle
• Only use pots with heat-resistant handles for boiling
• Be aware that boiled water usually tastes very different from tap water
• If you're worried about water used in juices/bottled drinks, stick to tea and coffee

Chemicals and tablets

Iodine and chlorine are fast-acting chemicals commonly used in water purification tablets. Iodine - sold in camping shops as a solution or crystals - is considered the better treatment. Both chemicals are safe if used properly.

• Always check how much of either chemical should be added per litre of water
• If you have a thyroid problem, ask a GP whether you can use iodine safely
• Water shouldn't be drunk for at least 20 minutes after a chemical is added
• To improve the taste of iodized water, add 50mg of vitamin C per litre

Filters

If you plan to use a filter, investigate what the sanitation will be like at your destination before you get there. Filters contain "pores" that let particles of different sizes through, so it's important to choose one that suits your needs.

• For protection against most bacteria, use a filter with pores no larger than 0.4 microns
• Filters with chemical-coated elements kill viruses found in heavily contaminated water
• Remember to sift out large particles of dirt if using a filter with very small pores

Medic Direct's Food and Drink section: http://www.medicdirect.co.uk