The water requirement of a performance horse is dependent on the amount of dry feed eaten, the environmental temperature and the amount of exercise the horse is performing. A good rule of thumb is 1.5 quarts of water per pound of dry feed. A 1000 lb performance horse will eat about 25 lbs of dry feed. This gives a water requirement of approximately 9 gallons.
As environmental temperature increase, the amount of water required increases. A temperature of 100 degrees Fahrenheit increased water requirement to approximately 20 gallons per day. Exercising a horse in hot weather further increased the water requirement.
Depending on the exercise intensity (amount of sweat produced), the water intake can increase more than 300% above a horse resting in a cool environment. The total water requirement would then be 25-30 gallons per day.