Your kidneys filter things from your blood, and they have since updated the water requirements to the number of ounces being 1/2 of your bodyweight (in pounds) of water daily. More if sweating profusely. I know this is a shitpost but you should drink enough that you pee every two hours while awake and your urine is light straw colored. The darker it is the more dehydrated you are. (Supplements and such for bodybuilders can drastically alter urine color)