It keeps the water moving and filtered, so it stays fresh and cool instead of flat. Fresh, flowing water naturally pulls a dog back to drink more often, and more sips across the day is the whole game. Both my dogs started drinking noticeably more the first week, no coaxing. And for the size of it, it does the work of three things I used to do by hand: refill, filter, and scrub. The stainless steel stays clean, and a rinse is all it takes.