Water is an important ingredient of the horse’s diet, since it is crucial for proper function of the body. This “nutrient” makes up 65 to 85 percent of a foal’s body weight, and about 68 to 72 percent of an adult horse’s body weight. A 1000 pound horse’s body contains about 80 gallons of water. Even small changes in total body water can have a negative impact on a horse’s health and well being. Water is contained within all body cells, between cells, and is an important component of blood, joint fluid and lymph.