Healthy people who consume moderate amounts of caffeine don't lose more fluid than people who don't have any caffeine. 1 A moderate amount of caffeine is about 200 to 300 milligrams a day. That's about two to four 8-ounce cups of coffee. You also get water through food. Some fruits and vegetables contain a lot of water, such as watermelon and lettuce. How much water do you need to drink every day? A common recommendation is to drink six or eight 8-ounce glasses of water or other fluid every day. But some adults may need more or less, depending on how healthy they are, how much they exercise, and how hot and dry the climate is. You may sometimes need to drink more water than usual if you: Exercise intensely, especially in a hot climate.