Water Needs for Individuals and Families
People need to drink at least one-half gallon (1–2 liters) of water per day (Wikipedia). Dehydration due to lack of water can result in death within 3 days (Wikipedia), or earlier if there’s fever and hence need of more water intake. In a pandemic context, water is needed to wash hands frequently. Failure to properly purify water can result in a variety of diseases including dysentery, which may be especially dangerous for children. Thus, having access to appropriate quantities of clean water is essential. During a pandemic, it is possible that water treatment plants may fail, at least some of the time. Thus, obtaining your own supply of clean water may be necessary.

For short periods of time, bottled water can be purchased and stored. However, this is an expensive and bulky solution, especially for families. Another solution for storing water is 55 gallon water drums. Another option is to store rainwater in barrels. Note, rainwater may not be safe to drink, depending on how and where it is collected.

If water treatment plants are offline for extended periods of time, water will have to be obtained from another source. It is a good idea to think of closest supply of water to you now. How will you transport it to your home? Bear in mind that gasoline may not be available.

Another reason to give water sanitation a lot of thought during a pandemic is that avian influenzas have been shown to spread from bird to bird in water.

From: Evolution and Ecology of Influenza A Viruses

Avian influenza viruses have been isolated from freshly deposited fecal material and from unconcentrated lake water. This information indicates that waterfowl have a very efficient way to transmit viruses; i.e., via fecal material in the water supply.

If people can transmit H5N1 in fecal material (there is evidence that it is present in this material), then its possible that if raw human sewage gets into the water supply, people may get infected in this way.

If wastewater and drinking water treatment plants are operating normally, this is unlikely to be a problem:

From, Cornell University ChronicleOnline, January 2, 2007:
A close relative of the highly pathogenic avian influenza virus (H5N1) can be eliminated by waste and drinking water treatments, including chlorination, ultraviolet (UV) radiation and bacterial digesters.

However, during a pandemic there is no guarantee the wastewater and drinking water treatment plants will be operating normally.

Whatever your source of water, you will want to purify it so that it is safe to drink. Here is some information from the EPA, CDC and FEMA on emergency water purification methods. You may also wish to purchase your own water purification devices. Camping and Outdoor stores are good places to shop for these. Major venders include Katadyn and Berkey. This description of Portable Water Purification in Wikipedia explains the different technologies.

Solar water disinfection (SODIS) is a cheap and easy way to disinfect water, if more advanced methods are not available.

From a series of flyers prepared by Melvin Johnson, Director, Lewiston-Nez Perce County Emergency Management:
Part 6 - Water (pdf)

A detailed description for obtaining a purifying water can be obtained here:
Water Treatment FAQ
by Patton Turner
Note: this was written in 1998 and it's description of available filtration systems is a bit dated.

http://homepage.mac.com/monotreme1/Prep ... idual.html