Q and A - Water Safety - Question

A.If the water was clean when it went into the containers, if the jugs were perfectly clean and sanitized to begin with, and if you are sure the containers were never opened, it will not have become unsafe to consume.

If you have doubts about any of these factors, the water can still be used if it is purified. The purification methods usually suggested are filtering followed by boiling or adding a few drops (about eight drops per two-liter bottle) of unscented liquid householdbleach.

Authorities like theRed Crossand theFederal Emergency Management Agencyrecommend keeping emergency water supplies on hand in case of a disaster: a gallon a day per household member, enough for at least three days. It should be either commercially bottled water or chlorinated tap water put into clean, food-grade, soft-drink-type plastic containers, not cardboard juice or milk containers.

The authorities also recommend renewing the supply every six months and keeping it away from heat and sunlight, which encourage the growth of any microbes that may be present. Boiled water can be aerated to make it more palatable by pouring water back and forth between two clean containers.C. CLAIBORNE RAY

Readers are invited to submit questions by mail to Question, Science Times, The New York Times, 620 8th Avenue, New York, N.Y. 10018, or by e-mail to question@nytimes.com. Questions of general interest will be answered in this column, but requests for medical advice cannot be honored and unpublished letters cannot be answered individually.

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