Our old dog waterer was a five gallon bottle inverted over a bowl. It worked great, but we were having to fill it up every few days. Not a big deal, I know, but we do ever strive for efficiency!
This new one is a metal basin that is filled from a hose. It has a float valve built in to maintain the water level at half full. Right now, we have the hose connected to a 30 gallon tank to test it out. We'll eventually connect it to a larger tank and gone will be the days of filling up dog water!