When your trying to get healthier, a piece of advice that is always suggested is to drink more water. But how much water is that, exactly? Many would say you should drink 8 cups (1 cup is 8 ounces; a total of 64 ounces) of water per day. But I've heard, from the internet and from people in real life, that it can be anywhere from a gallon (128 ounces) to up to half your body weight (yikes) per day. In my confusion, I did some research to find that the 8 cups rule originated from a study done in 1945 that found that it is ideal to drink 1mL of water per calorie of food you consume per day. Based on a 2000 calorie diet, this equates to 2000mL or roughly 64 ounces. More modern studies have come to the consensus that you should drink in a range between 1/2 ounce to an ounce of water for each pound you weigh per day. For example, a person who weighs 150 pounds should drink 75-150 ounces of water per day. Where you fall in that range depends on your climate, activity level, the amount of water in your food, and a plethora of other factors. If that's too complicated, a good rule of thumb is to drink water when you are thirsty.