Horses should have access to clean and fresh water at all times! Water is essential for life. In horses, water helps prevent colic and choke. Water helps keep the body functioning normally and helps kidney function. Did you know that if water is too hot or too cold a horse won't drink it? You can use tank heaters and heated or insulated buckets in the winter to help warm the water. Impaction colic is very common in cold winter areas. You might also need to utilize more salt in order to make them want to drink more. Did you know that horses do not have a mechanism that makes them want to drink water? Some commercial feeds have salt added into them, but you might need to supplement with additional salt or electrolytes.
A horse will drink anywhere from 5-10 gallons of water per day. A large horse, a horse in very active work, and nursing mares will typically drink more than that. It is important that water be kept clean and fresh. Not only will horses refuse to drink dirty or old water, but there might be bacteria or parasites in it such as pin worms or Leptospioris, which is the leading cause of recurring uveitis. Algae left in water buckets and water troughs can lead to poisoning if left to grow unchecked. For my water buckets in the barn, I dump them daily and refill them. I rinse them out daily, and they are thoroughly scrubbed every Monday, Wednesday and Friday. This schedule works well for me. I like to use the smaller water troughs so that I can dump them easily and give them fresh water. In the warm and hot months, I typically will dump out the warm water and give the horses fresh cool water. I scrub out my water troughs once per week.
It is important to know how much water your horse typically drinks. Horses that are suffering from a disease or illness may drink much more or less than normal. If you notice any changes in your horse's water intake, this will be a red flag that something might be going on.