1 Multiply by 2/3: Next you want to multiple your weight by 2/3 (or 67%) to determine how much water to drink daily. 2  For example, if you weighed 175 pounds you would multiple that by 2/3 and learn you should be drinking about 117 ounces of water every day. Drink 2 cups (16 oz) of water before every meal: Science has proven that drinking 2 cups of water before every meal helps you to eat less during meal time and lose weight. 2  If you do this three times daily-at breakfast, lunch, and dinner-you have already consumed 48 ounces of water.