put in 5 50 gallon rain barrels this spring. so far i've been able to maintain a 1000 sq ft garden with them. was at first surprised at how quickly they filled up. have never been lower than 50% so far, so i guess i could use the excess water for other uses if needed. nice to know. actually "dumping water". i guess if i wanted to figure in rainfall i could ,but dont want to get that involved w/ calculations. just a real world hands on experiment as it were. i am in south eastern va, , though, for informational purposes.