Easy rule of thumb to approximate water requires: Weight/2 = Ounces of Water
More accurately, it is between 0.6 and 0.7 per pound of body weight.
For example, using the mid point (0.65), a 200 lb guy would need to drink approx. 130 ounces.
You would really have to try to drink enough water to wash out your body to the point of danger, barring an unusual medical condition.