How much water do waterless urinals really save?

Green Living Image Gallery You flush cash and H2O down the drain each time you use a traditional urinal. See more green living pictures.

Waterless urinal. These two words might bring to mind an embarrassing problem that requires the help of a plumber before things in the bathroom get, well, worse. But actually, a waterless urinal is a type of urinal that is becoming more popular, especially as more and more businesses, public facilities and individuals look for ways to cut their budgets, go "green" or both. But exactly how much water can they save? We'll discuss that later, but first let's explain how they work.

The concept behind waterless urinals is surprisingly simple. The design of the bowl prevents urine from pooling and gathering. Instead, it flows down through small holes or a grating at the bottom of the bowl into a small reservoir called a trap. Inside this reservoir, the waste flows through a barrier of sealant, an oil-like liquid lighter than water that traps odors and prevents the urine from being exposed to air. Once underneath the sealant, the urine rests in a cylindrical well around a raised section of exposed pipe leading to the drainage line for the bathroom [source: Waterless]. (In some models, the drain line is off to one side.) Picture a straw puncturing the bottom of a paper cup.

As the waste rises higher than the top of the open drain pipe, the excess trickles down the drain. As more men use the urinal, the urine in the well continually flows out through the pipe as new urine displaces it. The urinals are designed in such a way that the flow of urine is continuous from the point it enters the trap until it enters the drain. This allows the waste to drain naturally, without needing to be forced out like a traditional urinal [source: Waterless].

Waterless urinals were actually invented back in the 1990s, but the recent push toward green construction has made them a more viable, commonplace option, not just a curiosity [source: Davis]. And the conservation potential of these somewhat odd urinals can be huge. Read on to find out just how much water they can save.