By Stephani L. Miller. Low-consumption gravity tank and pressure-assisted residential toilets have increased in efficiency over the last several years. To the relief of many homeowners, most pressure-assisted models have a quieter flush than earlier units, and many gravity models evacuate their bowls with only one flush. But not all low-consumption toilets are created equal.

The National Energy Policy Act of 1992 mandated a toilet manufacturing standard of 1.6 gallons per flush (GPF). But while the 1.6-GPF toilets helped save water, some generated a lot of consumer frustration.

"No one had put out any requirements for performance along with consumption requirements," says Paul DeBoo of Sloan Valve Co., maker of the Flushmate pressure-assisted technology that companies such as American Standard, Gerber, and Kohler incorporate into their pressure-assisted models. "So some manufacturers just dropped consumption without altering performance." Using less water without altering toilet engineering produces problems such as clogging, dirtier bowls, and the need for multiple flushes in gravity toilets. Too many trapway bends in pressure-assisted toilets inhibit effective waste evacuation.

Newer models of low-consumption toilets work more efficiently than their predecessors while conserving a precious resource. Courtesy Gerber Toilet manufacturers have learned to adjust design features and flushing systems to increase efficiency and performance in both flush types. "What we have learned by using computer aided design is to look at the entire toilet as a system and use the energy that is provided in a specific way," says Pete DeMarco, director of compliance engineering for American Standard. "In a gravity toilet all you have to work with is the gravity pressure." American Standard offers pressure-assisted and gravity tank toilets. "One of the things we look at is improving performance and the usability of the product in the marketplace," says Newbold Warden, marketing director for Toto, which offers four levels of performance in its line of toilets: standard gravity, gravity jet, tower gravity, and Gmax. Changes in a toilet's well contours, rim, and trapway size impact how effectively the water is pulled or pushed through the system. What most manufacturers have done, according to the Plumbing Manufacturers Institute, is enlarge trapway diameters and develop trapway geometry to produce stronger siphons, allowing waste to be evacuated more efficiently. Trapways in pressure-assisted toilets have been designed with fewer bends to reduce clogging.

Many manufacturers believe it's likely that water consumption regulations will be reduced even further. Some are approach ing the issue from a pro-active standpoint because, DeBoo says, "Nineteen states are under some level of severe drought and are limiting use of water. This is pushing consumption levels down even further in these states."

A 1999 study by the American Water Works Association of nearly 100 homes in 12 cities found that high efficiency toilets saved an average of 10-1/2 gallons per person each day. With these kinds of water savings, some manufacturers have already started to develop and test toilets that consume even less than 1.6 gallons. Stay tuned.