How much water should a horse have access to and how much does a horse drink? There are no simple answers to these questions as water requirements are affected by many factors, including environment, diet, body size, metabolic rate and even the fat content in the body. As an example, it has been shown that horses increase their water intake 15%-20% when the ambient temperature increases from 13°C to 25°C.
A “normal” horse requires approximately 50-60ml/kg body weight/day (25-30 litres/500kg) to replace the fluids required/excreted in the process of conducting basic bodily functions such as metabolism, respiration, and elimination of wastes from the body. If “water in” doesn’t equal “water out”, homeostasis (maintenance of the body’s equilibrium) cannot be maintained, and the horse will suffer if this inequity is not rectified in a timely manner.
Typically, in horses, water is obtained by voluntary consumption, predominantly from drinking but with a smaller quantity obtained from food intake. Water is lost from the body in urine, faeces, sweat and respiration. In the warm to hot weather, water lost through sweat can be 50-100% higher than it is during the winter, as horses rely on sweat to cool their bodies. Water lost via the respiratory system is low compared to water loss through sweating, defecating and urinating, but still needs to be considered when assessing fluid requirements and does increase in hot, humid weather. Manure contains a variable amount of water and can account for 30-55% of the water lost from the body, and will vary according to the diet.
Generally, horses on a high roughage diet will require more water than horses on a high grain diet. Bacteria resident in the hindgut require large volumes of water to break down the roughage ingested and produce nutrients from this roughage that the horse can absorb. Horses eating lush grass will appear to drink less when compared to a horse eating hay, however, this is because the horse eating lush grass obtains a greater part of his daily water requirement from the grass than the horse eating dry feed. Horses that are stabled or yarded have been found to drink most of their water intake within an hour or two of eating their feed, giving evidence to the close relationship between diet and water consumption.