Any treatise you’ve ever read on caring for horses probably includes the line, “Provide access to plenty of fresh, clean water.” Although we all understand that this is good advice–all living things need this simple, essential liquid–we don’t really tend to give water a lot of consideration as part of the equine diet. But, just any water source won’t do–it must be clean and palatable to the horse if he’s going to drink enough.

Water is the most important nutrient in the equine diet, bar none. Without water, almost all of your horse’s systems cease to function. It would be virtually impossible to list all the ways in which water is essential–but just to name a few, it:

• Aids in thermoregulation (maintenance of the horse’s body temperature);
  
• Lubricates the joints;
  
• Helps cushion the central nervous system;
  
• Is involved in both sight and hearing;
  
• Aids in digestion;
  
• Acts as a solvent for toxins and helps eliminate them through urine and sweat; and
  
• Helps maintain an elastic skin tone.

To give you another perspective on water’s importance, consider that horses can survive without food for up to three weeks, but they can only survive without water for a maximum of five to six days. Although water intake varies according to the horse’s exertion level, the ambient temperature, the components of his diet (more on this later), and whether or not the animal is pregnant or lactating, the average 1,000-pound horse needs a bare minimum of three to eight gallons a day to function at a maintenance level.

When water intake is restricted–whether because water isn’t made available, the horse finds it difficult to drink or swallow (for example, if he is suffering from a broken jaw or any of a number of diseases), or the available water isn’t very palatable, a horse quickly becomes dehydrated. Within 24 hours of water deprivation, a horse can lose about 4% of his body weight. After 48 hours without water, 6.8% of his body weight will be lost, and after 72 hours it’s about 9%. If summer heat is involved, that number can skyrocket to 16%