Alot of it depends on your activity level. The average person should be drinking 8 8oz glasses a day to maintain what your body (which is primarily composed of water) needs to properly maintain. If you are doing exercise and very active, that number is going to be too low for you and you would need to drink more. I drink about 4 24oz bottles of water a day and have been for about 5 months now and it has done nothing but help me.
Here is what I found on-line:
The kidneys of a healthy adult can process fifteen liters of water a day! 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. You may need more water if the weather is very warm or very dry, if you are exercising, 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.