When a horse drinks, it will put its muzzle into the water and open its lips. It is important that no air can be taken in, so just the center point of the lips are pursed to create an opening.
Most horses know exactly how much water to drink to keep themselves well hydrated. However, there are some situations where a horse may drink too much.
It is unlikely that a horse will stop drinking to the extent that he becomes dehydrated unless he is sick. However, you need to monitor your horse’s water intake as dehydration can occur in a short space of time.
Horses drink water by pursing their lips and using their tongue to create an area of low pressure that pulls water into the mouth. This then triggers the swallowing reflex.