In hot climates the need for water doubles or triples.
Hikers require a gallon or more per day as they sweat and respire water and water vapor.
Note that alcohol and caffeinated drinks have a dehydrating effect. A good indicator of semi-dehydration is chapped lips. The next time your lips feel chapped drink several glasses of water and see what happens. As visible semi-mucous membranes, lips are a good indicator of your state of hydration. 1 Thirst is not a reliable indicator.