It is important to drink a lot of water. As your body breaks down fat, it is important to flush the unused ketones from your body. A general rule of thumb is 64 oz. plus 8 oz. for every 25 lbs. of weight you want to lose. Another approximation is to divide you body weight in half. Both methods of determining the amount of water to drink will make sure you are drinking enough. However, if you are thirsty, or not sure if you are drinking enough water, then you are probably not. Drink more. You can't drink too much water.