Horses and Water
A full size horse (e.g. 500kg or 1100 pounds) drinks about 30 liters (6 gallons USA or 5 gallons UK/Canada) per day. However this amount can vary by 50% or more depending on:
Due to all these variables, the actual amount of water a horse requires on any given day can be much more or much less than the theoretical average. The best advice is to make sure that your horse has regular access to water, that it is heating above freezing in winter, and that one tries to observe any unexpected change in the amount a horse is drinking.
Horse buckets, drinkers and troughs should be cleaned on a regular basis. In particular, rotting or fermenting food should be removed promptly and the water replaced, since polluted water can result in horse illnesses.
If the pastures have streams or ponds, these should be fenced off if the water is not clean, to avoid potential illnesses. Even if the water is clean, any unsafe access points (e.g. steep or slippery slopes) should be fenced off to protect the horses from injury.
If the water is heated, any electrical cables and connections should be protected to avoid horses chewing on them or damaging them, for the protection of both equipment and horse. If electrical cables are subject to wear or movement, they should be inspected periodically to ensure that they are are still safe and functional, in particular that there is no risk of short-circuiting.
Horses should normally have free access to water at all times, especially if they are eating dry food (such as hay) or during hot weather.
One exception to this is that after heavy exercise or work they should not be allowed to drink too much water until they cool down, as suddenly drinking large amounts of water on a hot stomach can result in colic. Another exception is that if a horse has been deprived of water during winter temperatures (e.g. if their drinker or water bucket has frozen), they should not be allowed to drink a large quantity of cold water at once as drinking lots of cold water quickly. In both cases one should provide only a moderate amount of water, then wait half an hour before providing more water.
To prevent horses being deprived from water during freezing temperatures, one should protect water pipes. It their drinkers are prone to freezing, one should use a heated water bucket or heated drinker.