depends how deep it is
An estimated 250,000,000,000,000 a year.
460 trillion gallons
one gallon per day per sq meter
1 acre = 43560 sq.feet. 1 foot deep water over an acre is 43560 cubic feet, which is 325851.4 gallons in 1 foot deep. If it is 1 inch deep (1/12 foot) then it is 27154.3 gallons in 1 inch deep.