Every horse, no matter what breed has different dietary requirements. Like say in a group of dogs, one dog, may keep returning to a water bowl, but will only take it if it needs it, another, of the same breed, height, weight, will only drink from it once or twice, it's pretty much the same with horses. Give them water, and they will only take what they need at each given time, this is not dependable on the breed, size or any physical things, it's just that they are all different. It's a good idea (on the assumption that yours is stabled) Just to give a big 25L bucket, and he or she will take whatever it needs, don't be too worried about how much she or he does or doesn't drink, but if it is a silly amount, that's unusual for it, then you may bneed to consult someone, as it may be something intestinal (not that this is the case)

:) X

you will generally find bigger horses drink more than smaller ones, and if a horse has been worked it will drink more than a horse that has been rested all day.

Each Horses water requirements are different even in the same breed, also depends on what you are feeding, age, health, amount of exercise, type of day, if lives in or out. Difficult to define but easy things can be caught are horses not drinking or too much, a horse can drink up to 14 gallon a day.