Tanker water safety: storage, cleaning and disinfecting

When piped supply runs short, many homes rely on tankers. The water is only as safe as the tanker and the tank it ends up in.

Clean the tank. The World Health Organization's technical note on water storage tanks and tankers sets out the basic steps: empty the tank, scrub the walls and floor to remove silt and slime, rinse and drain the dirty water away, then disinfect with chlorine and flush before use. Keep tanks covered, with a lockable lid on the access point.

A simple chlorine dose (fact). Chennai Metrowater (CMWSSB) advises adding bleaching powder with 25% available chlorine at 10 milligrams per litre, which is 10 grams per 1,000 litres. Mix it well and wait 30 minutes before using the water. Boiling also disinfects, so boil water you plan to drink if you are unsure of its source.

The tanker itself. WHO advises that drinking water should only go in tanks that have held food-grade liquids; tanks that have held fuel or sewage should not be used. If tanker water smells, tastes odd or looks cloudy, do not drink it and tell your supplier and the local water board.

Testing. Water boards and approved labs can test samples for bacteria such as E. coli. Ask yours how to get a sample checked.

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