A quick check on
http://www.peacecorps.gov/WWS/water/...eog01sup01.pdf
shows that 10 gallons per day per capita is about average for w.
africa. US is closer to 200 gallons per day per capita. But in an
emergency, one has to learn to change lifestyles quick.

"per capita" water usage numbers can be very misleading, though,
since they usually include things that aren't really domestic
water-use. As an example: from
http://www.pepps.fsu.edu/safe/pdf/sc1.pdf

"Per capita water use is calculated by dividing the total
public supplied water in gallons per day by the population
served for each state. The water withdrawn from public water
suppliers includes all waters withdrawn by public and private
water suppliers and delivered to multiple users for domestic,
commercial, industrial, and thermoelectric power uses, as
well as water lost in collection and distribution systems,
public use (water for fire fighting, street washing,
municipal parks, and swimming pools), and water transferred
between adjacent states or water-resources regions.
This differs from total water use since it does not include
irrigation and agriculture."

That page give figures that range from 83 to 575 US Statute
gallons (300 to 2200 litres) per person, across assorted
states and years, but I distrust the "not include
irrigation and agriculture", claim, since it almost
certainly DOES include irrigation for lawns and household
gardens. It doesn't say whether they estimate individual
wells for single-unit dwellings. I suspect not.

--Goedjn