That depends on several factors. Including how much annual rainfall an area gets, as well as how much avg evaporation an area gets. Those are just a few factors that determine how much runoff acreage is needed to keep a one acre pond full.

For example in our area of North Texas. (We are about 80 north of Dallas) we get an avg of 60 inches of rain a year and avg evaporation is around 70-80 inches a year. It takes around 8 acres of runoff to keep a one acre pond full. Go further in East Texas you need 4-6 acres of runoff per acre. Go to deep west Texas and it might take 15-18 acres of runoff to keep a 1 acre pond full. I'm sure there have been some former posts about it. It is also discussed in Bobs book and there is a NRCS document here in Texas that goes to great lengths discussing it. When time comes let me know I'd be happy to help you get that information.

Fisheries Biologist, Texoma Hatchery.
www.texomahatchery.com