Horses should not be fed excessively cold water, as it may bring on colic symptoms. Try a heated waterer or consider taking warm buckets out when it's cold outside. If nothing else, make sure to break the ice on a horse's water supply in freezing temperatures. In very cold weather, water heaters may be needed to prevent the water from freezing. If you are using a submergible electric water heater to keep the water supply open and free of ice, check to see if it is giving off stray voltage and shocking the horses when trying to drink. Be careful that you do not get shocked. If you use automatic waters be sure the heating element is turned on and that there is no stray voltage.
Water performs many tasks in the body. It makes up most of the blood that carries nutrients to cells and takes waste products away. In addition, water is the body's built-in cooling system; it regulates body heat and acts as a lubricant. A horse drinks about 10 to 12 gallons of water daily depending on the work it is doing. Larger breeds of horses may drink up to 15 to 20 gallons of water a day. Horses that are not drinking enough water will reduce their feed intake and reduce the energy intake.
During the bitter cold weather is when horses need to keep up their energy sources and the worst possible thing that can happen is to have a horse quit drinking water and go off feed. If the horse cannot drink or worse cannot get to water because it is frozen solid, the horse 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%. Symptoms of dehydration are dry mucous membranes, sunken eyes, tucked-up appearance, skin that has lost its elasticity, and a slowed capillary refill time and a depressed attitude.
These signs become obvious when the horse has already lost 6% of his body weight or more, by which time dehydration has already begun affecting digestive efficiency. When this happens the body cannot maintain a constant body temperature and become hypothermic.
But the worst risk caused by lack of water is that the horse's intestines become impacted and results in colic. In fact, the main reason the incidence of colic increases from December to March is that many horses don't drink enough water in the winter months.