I have two horses now but for years had more. First I have a box where I can run the pump with the generator. I also store over 500 gallons in various troughs and closed 55 gallon water containers. In the heat of the summer any open trough has to be cleaned often. So I highly recommend at least a few closed barrels. Unless it's spring time with lots of grass they will drink over 10 gallons per day. Spring grass in my neck of the woods has lots of water in it and they cut way down when on the grass. They actually drink a lot in the winter as they are eating dry hay and feed.