The general medical consensus on the amount of water to drink is about two quarts (6 – 8 glasses) per day. Hot climates and/or vigorous exercising will require more.
The trick is to watch the amount of pee-pee going out. Notice the frequency and color of your urine. Generally, if you are drinking enough water and regularly pee-pee the color of the urine will be clear or a very pale yellow. If your pee-pee comes out infrequently or the color is bright or dark yellow, your body needs more fresh water.