They are actually designed for places like commercial buildings where there are lots of rest rooms and a corresponding sized water bill. Since water (in my area) is billed going into the house AND again coming out, because they assume that it must go out of the house to a waste treatment plant, it is a way to save real money over the long haul. Here's a website I copied to give you a look:
Falcon, Sloan Valve, and ZeroFlush WaterFree Urinals & Cartridges