A good rule of thumb is to consume 32 ounces at every meal.  If you happen to be on a low calorie diet, drinking water can help alleviate the feelings of hunger, but can you drink too much?  Typically the answer to that question is no, and you should always consult your doctor if you are concerned for any reason. If you have kidney or adrenal problems, or if you’re taking diuretics, consulting a physician about your water intake is crucial.  Don’t drink all of the water at once — drink several glasses of water throughout the day. Of course hydrating during intense exercise, like PED’s or PER’s, is essential to maintaining your stamina and warding off fatigue.  If you are waiting to drink when you are thirsty during a long bike ride or run, it is difficult to stay ahead of water loss.  Always hydrate while exercises at a rate a little faster than you truly think you need to.  Also remember that if caffeine is a major part of your diet, then you will need to increase your water consumption; coffee, tea, and other caffeine laden drinks are great sources of a pick-me-up, but they’re also a diuretic. Temperature and humidity are also concerns: make sure that on hot, humid days you increase the amount of water you consume accordingly.

Sources:

Centers for Disease Control and Prevention. “Tips for Preventing Heat-Related Illness.” http://www.bt.cdc.gov/disasters/extremeheat/heattips.asp.

Institute of Medicine. “Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate.” http://www.iom.edu/?id=18495.