UA Study Shows Leaks in Conservation Theory Behind Low-Flow Toilets

Oct. 31, 2000

The low consumption or “low flush” toilet has been a fact of life in some American homes for over a decade now. Some communities and states began mandating their usage in the late 1980s, and in 1992 modifications to federal law mandated this water saving technology.

A new report by two researchers at the University of Arizona in Tucson concludes that, despite the skepticism that greeted their introduction and a history of early problems, most low-consumption toilets are doing their job. Unfortunately, the research also shows that, over time, a significant fraction of the anticipated water savings is lost due to poor toilet design and performance modifications. Some of the modifications are inadvertent on the part of homeowners.

Jim Henderson and Gary Woodard, then with the Water Resources Research Center at the University of Arizona, studied 170 households which participated in a Tucson Water rebate program to encourage replacement of older toilets with 1.6 gallon low- consumption models. Toilets studied were purchased between 1991 and 1992, just a few years after the low consumption toilet was introduced into the American market.

The report was prepared for the Water Conservation Office of the City of Phoenix Water Services Department, and the U. S. Bureau of Reclamation. The researchers installed special devices called data loggers on these homes to monitor the amount of water used by the then seven-year-old toilets. Combined with surveys of more than half of the households, the study revealed some problems with the aging toilets.

Nearly half of the low-consumption toilets in the study had problems with high flush volumes, frequent double flushing and/or flapper leaks. The average flush volume for all of the toilets was 1.98 gallons of water per flush, or about 24 percent higher than the 1.6 gallon maximum they were designed to use. About a quarter of the households had at least one low-consumption toilet that averaged more than 2.2 gallons per flush.

Several companies manufacture low-consumption toilets, and some makes and models performed better than others. Also, the survey of homeowners also revealed a range of performance and satisfaction.

Henderson and Woodard's study reports that some of the problems with low-consumption toilets were traced to how manufacturers designed their products. The industry's standard was set at 1.6 gallons and companies were free to achieve it any way they chose. That standard, developed in 1990 by the American Society of Mechanical Engineers, was adopted in local, state and national construction codes.

Most manufacturers kept the 3.5 gallon tanks but adjusted the inner workings to achieve a smaller flush, either by using a proprietary early-close flush valve flapper, or a toilet dam. Intentional or inadvertent replacement of a proprietary flapper valve, or removal of the restriction dam can cause a marked increase in water use.

A few manufacturers opted to use a pressurized flush technology that uses a sealed bladder and captures household water pressure. These toilets are also noisier and more expensive. Other manufacturers went with different unique designs.

Henderson and Woodard's data logging method revealed a range of water fixture leaks and problems, including constant leaks and flushing at a repeating, constant interval. Certain brands of in-tank toilet bowl cleaners also may have contributed to mechanical problems with toilets.

“This report confirms the worst fears the water industry has had about these products — that long-term savings are not reliable,” said Tom Babcock, Lead Water Resource Specialist for the City of Phoenix. “Unless manufacturers address these concerns, unless the standard is made tighter, we'd be foolish to bank on this savings in making forecasts of future water demand.”

The report recommends that the design of low-consumption toilets be modified to reduce deliberate and inadvertent alterations of the flush mechanism that increase water use. The authors also recommend that water providers not offer rebates, or purchase as part of direct install programs, any toilets with alterable designs or with specialized parts for which replacements are not readily available.