When the first 1.6 gallons per flush (GPF) toilets were introduced and installed in homes, both gravity-tank and pressure-assisted, consumers experienced a lot of frustration with the efficiency and performance. The 1992 National Energy Policy Act mandated the 1.6 GPF toilet manufacturing standard for both gravity- and pressure-assisted toilets, but the act focused only on consumption.

"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 manufacturers 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 produced problems such as clogging, dirtier bowls, and the need for multiple flushes in gravity models. Pressure-assisted models were also loud, and the velocity of the flush caused the water to splash.

Manufacturers of both flush types have since learned to adjust design features and flushing systems to increase efficiency. "In order to make these things efficient," says Pete DeMarco, director of compliance engineering for American Standard, "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. In a gravity toilet, all you have to work with is the gravity pressure." American Standard offers both pressure-assisted and gravity-tank toilets.

"Virtually everything about the bowl and tank -- except minor design lines -- will impact the overall performance of the toilet," says Kevin McJoynt, director of marketing for Gerber Plumbing, maker of the AquaSaver gravity and the Ultra Flush line of pressure-assisted flush toilets. Redesigning the size, shape, and angle of trapways, the location and direction of rim and jet holes, and tank and bowl water levels have improved siphons in gravity toilets. Trapways in pressure-assisted toilets have been designed with fewer bends to reduce clogging.

As a result, efficiency and performance have improved in both flush types. To the relief of homeowners, many pressure-assisted toilets now have a quieter flush than earlier models, and many gravity toilets are now able to evacuate their bowls in one flush.

Newer models of low-consumption toilets work more efficiently than their predecessors.
Courtesy Toto Newer models of low-consumption toilets work more efficiently than their predecessors.

The next big move in toilet design will be to reduce water consumption even more. Many manufacturers believe it is likely that water consumption regulations will be reduced further, although some doubt that a federal mandate will be issued. Manufacturers such as Toto, St. Thomas Creations, Sloan Valve, and others are approaching the issue from a proactive standpoint because, says DeBoo, "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 found that high efficiency toilets can save an average of 10 1/2 gallons of water per person each day. With these kinds of savings, and with drought conditions across the nation a growing concern, some manufacturers have already started to develop and test toilets that consume less than 1.6 gallons. Stay tuned.