Ask the experts: Bleaching water

Q: "Will a few drops of Janola (or any other bleach) enable unsuitable, or perhaps water from unknown origins, to be used as drinking water? This would be in an emergency only."

A: Bronwen King, author of 'Survive bird flu and other disasters', responds:

"The answer to your question is yes! Chlorination has long been used as a way of making water safe for drinking, and chlorine is produced by the active ingredient in household bleach, sodium hypochlorite. Household bleach is therefore very useful to include in any kit for emergency situations.

When choosing your bleach, check the label; you want one that has at least 4% sodium hypochlorite. It is also wise to avoid bleaches that contain colourings or perfume. Water experts recommend using 3 drops of bleach per litre of water (an eye dropper is useful here). This works out to be 1/2 teaspoon per 10 litres of water. Stir or shake the water after bleach has been added, and leave to stand for 30 minutes.

As the chlorine works, it is used up and so loses much of its smell. The treated water should smell slightly of chlorine to indicate that the impurities have been removed and it is safe to drink. If it doesn't have a slight chlorine smell, repeat the dosage and stand for a further 30 minutes. After this if it still does not smell slightly of chlorine, consider the water unsuitable for drinking and use for washing purposes only."