Is my horse drinking enough?
There isn't one correct gallon number for every horse. Start with access, conditions and your horse's normal intake.
Quick answer
University of Minnesota Extension says a typical 1,000-lb adult horse often drinks roughly 10–12 gallons per day, but needs vary with feed, temperature, humidity, exercise, sweating, lactation and other factors.
Unlimited access to clean, fresh water is more important than trying to force every horse into one target number.
Winter deserves extra attention
Dry winter hay contains far less moisture than lush pasture, while cold water or frozen sources can discourage intake. UMN recommends keeping winter drinking water available and notes that moderately warmed water can encourage drinking.
Watch for change
If you can measure intake, compare the horse with its own normal pattern. A meaningful drop is useful information even when today's gallons still fall inside a broad population range.
With a shared trough you can measure herd consumption, but you cannot know one horse's intake without observing or measuring that horse individually.
When low intake matters
Poor water intake can contribute to dehydration, reduced feed intake and impaction colic. Contact your veterinarian when low intake is accompanied by illness, colic signs, marked lethargy or other concerning changes.
Sources
University of Minnesota Extension: Caring for your horse in winter
University of Minnesota Extension: Encouraging your horse to drink
University of Minnesota Extension: Feeding the mature horse
Educational information only and not a dehydration diagnosis.