This depends on a number of variables. The normal recommendation is 1/2 of your body weight in ounces a day. So if you weigh 150 lbs, you should drink 75 oz of water. If you work out, if it’s hot and you’re sweating more, if you fly, if you have a soda/coffee/tea, then you can choose to drink more. All of those things speed up the elimination of water and we therefore need more.