See those Egrets (cowbirds) in that picture? On occasion, I can have a hundred of those in my yard. Usually after a heavy rain.
Those ponies, not horses, living there drink twice as much water as do normal horses. It is to purge out the high level of salt that they consume......also, the source of their characteristic 'pooch belly'.
"The most obvious difference between a horse and a pony is size. For most purposes, a pony is under 14.2 hands high if you ride English, and under 14 hands if you’re a western rider."
Horses are 15 hands are more.
Whether pony or horse, they are all Equus caballus.