Getting enough water sounds elementary doesn’t it. But for horses, and cattle, as well,
. . . water is the most important nutrient, especially in hot weather. Without it, horses die within a few days, whereas they may be able to go weeks without food.
Source: BEEF, June 25, 2018. Link.
Ambient temperature affects water intake, and horses typically drink less water in cold weather, while heat and humidity increase their water requirements. Depending on the conditions in which a horse is exercised, water intake can increase to as high as 30 gallons per day.
Also see: Water + horses search results, Animal Health Digest. Link. In addition to other water related topics, Threats in the water for horses, June 21, 2016. Link. addresses diseases caused by organisms that thrive in ponds, streams and marshes