When I lived in that swamp called Fargo I had a water powered sump pump back up, the brand was Liberty. Luckily it was never called up to bat, but I would test it on occasion to make sure it worked. Like Ahab said they could cause a water problem since there is constant water pressure going to the unit, solid installation is key. They don't pump as fast as a battery back up either, (don't quote me on this) but I want to say for every 10 gallons of water going though the sump pump it will pump 1 gallon out. I'd put in another one if I had to though, not dealing with a battery was nice.