According to the American Animal Hospital Association, average animals need 28ml per lb per day. If you do that math, round, and convert, that ends up to about 10 cups per day for an 80lb dog (
http://www.healthypet.com/library_view.aspx?ID=128&sid=1 ). You have to keep in mind though that if it is hot or he has been active, that number will increase. You also have to make sure to spread the water out throughout the day so he doesn't 'camel' it and have way more than he needs at once.
That being said, most dogs will drink only what they need, so when you feel confident in his housetraining, I would make sure that he always has fresh water down. Until then, I would say its ok to limit his water to about 10 cups a day
unless he is particularly thirsty (from playing, excersizing, chewing something salty, being hot, etc).
We keep zoey's water bowl full now, and she will drink little bits at a time throughout the day, except when she has been out excersizing or playing (during really rowdy play sessions, it is not unheard of for her to go through 2 big bowls
). When she was a puppy we would limit her water, but she learned how to tell us she was thirsty.... It's funny, she used to get frequent baths in the tub, so she thought of the tub as 'the water place' and when she was really thirsty she would climb into the tub to tell us. She is so silly
Now when she is thirsty and the bowl is empty, she will stare at us until we notice, and scratch at the bathmat under it if that doesn't work.