The kidneys of a healthy adult can process fifteen liters of water a day, so you are unlikely to suffer from water intoxication, even if you drink a lot of water, as long as you drink over time as opposed to intaking an enormous volume at one time. As a general guideline, most adults need about three quarts of fluid each day. Much of that water comes from food, so 8-12 eight ounce glasses a day is a common recommended intake for an active person. You may need more water if the weather is very warm or very dry, if you are exercising a lot, or if you are taking certain medications. The bottom line is this: it's possible to drink too much water, but unless you are running a marathon or an infant, water intoxication is a very uncommon condition. Drinking too much water increases the sodium requirement also.