Waterless urinals have come into fashion due to growing concerns about water conservation. Although generally only useful for male public washroom use, waterless urinals, with their intriguing design, can nevertheless save large amounts of water.
Waterless urinals use one of two broad types of design: a one-way valve system, using either a rubber tube seal or a curtain valve seal, or a sealant liquid system. The sealant liquid system, in turn, may employ replaceable cartridges that are pre-filled with sealant liquid, or the liquid is introduced into the drain hole and settles into position.
The function of the various types of waterless urinal is to allow urine to flow through the urinal into the sewer or storage system without allowing odor to escape into the room. The rubber seal system uses a rubber tube that is flat on the bottom when not in use, serving as a block, but opens up when urine is flowing through. The curtain valve seal works similarly, except that its design employs hydrodynamic laws that give it "self-cleaning properties." A small pressure difference causes the urine to wet the whole inner surface between the curtains, flushing them clean instead of allowing urine precipitates or sludge to build up. The blocking fluid system, which uses vegetable oil or specialized oils for the sealant liquid, relies on the different densities of urine and oil. The urine sinks through the liquid, which floats on top of the urine layer, blocking odor. Under current United States legislation, only liquid sealant systems are approved, according to the 2009 Water, Engineering and Development Centre (WEDC) conference paper "Waterless Urinals: A Proposal to Save Water and Recover Urine Nutrients in Africa," by E. v. Münch and P. Dahm.
To achieve their odor-free performance, waterless urinals have other requirements in addition to their odor-blocking systems, according to the WEDC paper. The urinal bowl surface must be smooth and non-stick by using, for example, wax coatings. The connection between the urinal bowl and the drain fitting must be correctly designed to minimize crevices where urine can accumulate, and thorough maintenance regarding the bowl and odor blocking devices must be observed. The surface of the bowl must be wiped clean once or several times per day, while maintenance of the odor blocking devices depends on the system.
In the United States, the main benefit of waterless urinal units is their conservation of water. Up to 20 per cent of the world's available drinking water is wastefully flushed down the drain by the use of flushable toilets and urinals, according to the website of Waterless, a company that produces a type of waterless urinal. In the United States alone, approximately 8 million urinals are installed with approximately 100 million men using them, the company estimates. This would mean that the potable water use of urinals in the United States, assuming an average two-gallon flush, is equivalent to the water use of 490,000 homes. Between 20,000 and 45,000 gallons of water per year can be saved by a waterless urinal, according to the company. The Federal Energy Management Program estimates the yearly water use of a three-gallon flush urinal (those installed before 1992) at 23,400 gallons based on 30 flushes per day, 260 days per year, according to Facilities Net.com.
Regulatory and facility managers once stood as barriers to the adoption of waterless urinals, but the devices are becoming increasingly popular with education on their benefits, safety and easy maintenance and the advancement of the green building movement, according to a 2007 post on Greenline Blog.com.