You can't have too much water. My birds have access to fresh water 24/7. They have water in their coops and outside too. I have never figgured out how much water my birds drink. I refill their waterers daily. I'm guessing 40 birds drink 10 MOL gals of water a day.
I have about 20 birds and only have to carry water in the winter. The bare minimum to keep them with something all day is 2 gallons...in the winter. In the summer they have a float valve in the water bucket so it stays full all the time.