A general rule of thumb is to try to drink a gallon of water per day—but needs can be somewhat higher for larger people or those who sweat a lot due to intense exercise, a heavy labor job, or living in a hot environment.
It’s not a good idea to drink more than 2 gallons, as doing so could dilute blood electrolyte levels (sodium and potassium), causing cramping, heart palpitations, and other adverse effects.