Experts say that you should drink at least eight glasses of water every day; a glass of water is about 8 ounces US or about .236 milliliters. That estimate assumes that your environment is normally cool, you are about 150 pounds or about 68 kilograms, and exercise in some form, about 20 minutes a day. Recent studies have revealed that there is no set requirement of water per day. You should drink when you are thirsty.