Hatha yoga is a moderately-paced, catch-all name for the vast menu of poses that are practiced wherever you can roll out a sticky mat.
An 1100 lb horse on a dry forage diet at an average temperature of 68 degrees Fahrenheit will need a minimum of 6-7 gallons of water per day or 48-56 lbs of water, and many horses will drink more water than the minimum.
If you horse is dehydrated, call a vet ASAP. A horse will drink 5-10 gallons a water per day in the winter, 10-15 in the summer.