A "glass" is 8 ounces. But I have seen recommendations from several fitness sources that the amount necessary is 1/2 ounce for each pound of your body weight (or an amount in ounces equal to half your weight in pounds.) For me, that would be about 52 ounces, or 6 1/2 cups). Obviously, more water than "necessary" can't be a bad thing, but plain water is really, really hard for me to drink. I drink 8-10 cups of hot tea a day, some water and some coffee. (I don't use cream or sugar.) I HOPE I am getting enough "water" this way. By the way, the tea tracks as 2 calories per cup, but green tea tracks as 0. I drink about half in green tea.