According to Dr. Laura Pylman, DVM, at Mid-Michigan Equine Services, PLLC, in Laingsburg, Michigan, the basic water requirement for an average size horse is about 30 liters, or just under 8 gallons of water per day. The amount of water that an individual horse needs daily depends on several factors, including: The horse’s diet Their weight Their age Their activity level The climate (temperature and humidity level) of their environment Dr. Pylman says that certain health conditions, such as lactation in mares or Cushing’s disease, can also play a role in how much water an individual horse needs to drink daily.,Jump to section How Much Water Do Horses Need? Horse Watering Supplies Dehydration in Horses Horse Watering Tips for Cold Weather Horse Watering Tips for Hot Weather Horse Watering Tips for Traveling FAQs About Watering Horses