Rangers recommend one gallon of water for an eight-hour hike in hot weather.
If it's hot, try soaking your clothing in water for refreshing coolness. An easy pace allows the body to function more efficiently and feel better. AND the weather is cool. The Canyon Rule is to allow one-third of the time and energy on the descent and the rest for the climb back up. Wind and rain can cause hypothermia even in summer, so raingear can save the day year-round.