Crisis of drinking water

Understandably, lack of safe drinking water is the main cause of widespread diarrohoea in the flood-affected areas in Bangladesh. Flood in Bangladesh, among other things, is always associated with monsoon rain, and I do not understand why the ICDDR,B or the Disaster Management Bureau does not advise the flood-marooned people to store rainwater for drinking and cooking purposes during the crisis period lasting hardly one to two weeks. This is probably the safest source of water (after a couple of minutes of shower) at hand in such a situation.
It may be mentioned here that almost the entire requirement of freshwater for drinking and cooking is met from storing rainwater in the Maldives.