20 gallons a day per person, all purposes
7 gallons a day per horse, drinking
5-6 gallons a day per cow, drinking

Reccomendation is a 3-4 day supply

(This is from _Farm Machinery_ "Practical Hints for Handy-Men", ISBN 1-55821-951-x)

Of course, this assumes normal day to day operation--in survival mode, drinking water/sponge bath only, a person in a hot climate can (and has!) consumed as much as twelve liters a day. Of course, at the time, I was not acclimated to the heat/humidity of the region....
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Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, a critter that can be killed but can't be tamed. --Robert A. Heinlein