Going With the Flow--1.6 gpf Toilets That Work

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Few efficiency standards have generated as many jokes and complaints as the 1.6 gallons per flush (6 liter) toilet requirement. The Energy Policy Act of 1992 required manufacturers to reduce the quantity of water per flush to 1.6 by 1994. Some say the industry was caught off guard and was given insufficient time to re-engineer their models, others say they not only had enough time, they should have seen the new standard coming (Massachusetts and California already had such a standard in place). In any event, the new requirement has been widely blamed for performance problems with some low-flow toilets. User unhappiness with toilet performance led to Congressman Joe Knollenberg (Republican – Michigan) sponsoring legislation to repeal the standard last year (see EBN Vol. 8, No. 9). So, are there low-flow toilets that work, and if so, how can they be identified? The answer is a resounding “yes” to the first question and “help is on the way” to the second.


The fluid dynamics are more critical at 1.6 gallons per flush (6 lpf) than at 3.5 gpf (13 lpf). All aspects of operation must work in concert for optimal performance.

Source: Toto USA

There are two ways to identify toilets that work. The first is through standardized testing—a responsibility that falls to the American Society of Mechanical Engineers (ASME). ASME’s standards committee A112 – Plumbing Materials and Equipment currently has a Project Team 19.6 (Hydraulic Performance for Water Closets and Urinals) working on new minimum performance standards for the “flushability” of toilets—standards that are specifically referenced in the federal legislation. Mr. Thomas Konen, chair of the ASME Project Team, told EBN that “the hydraulic performance of the 1.6 toilets is so different from the 3.5’s that new standards are definitely needed. We are just getting back test results now that I am confident will result in new and better standards of performance.” Manufacturers have been testing the new standards—there are issues such as the variability of results and the best test media to simulate human waste and the wide range of tissues used. Project Team 19.6 met in Washington, D.C. in mid-August and approved new standards for ASME balloting. The advantage of this type of performance assurance is that, if they are stringent enough, the ASME minimum performance standards will force adequate flushability upon all toilets by federal mandate. The disadvantage is that, if the standards are not rigorous enough, poor performers may remain in the marketplace.

The second way to identify toilets that work is to survey users or plumbers. Plenty of scientific and anecdotal information has been collected on toilet performance. Scientific surveys of users have been conducted by the cities of Los Angeles and New York (New York’s included licensed plumbers as well) and by the Metropolitan Water District of Southern California. See table below for a list of the top performers from these three surveys—comparisons are difficult among the surveys because of variations in models, questions asked in the survey, and number and type of respondents. Note that a “low” ranking does not necessarily translate into significantly lower performance—often overall ratings were separated by very small differences.

Survey Results for Toilet Performance


Sources : “Ultra-Low-Flush Toilets – Customer Satisfaction Survey,” Metropolitan Water District of Southern California; “Evaluation of New York City’s Toilet Rebate Program – Customer Satisfaction Survey,” New York City Department of Environmental Protection; “A Survey of Ultra-Low-Flush Toilet Users,” Los Angeles Department of Water and Power

Anecdotal information has been collected from consumers, plumbers, and water management professionals. A look at various Web sites on the topic of low-flow toilets brings up the same names for high performance: Toto Kiki (most, if not all, models), American Standard (Cadet), and Western Pottery (Arris), among others. The Kohler Wellworth, which we have been happy with at the EBN office, appears on both good and fair lists. (Several EBN staff members also report good performance from the Wellworth toilets in their homes.)

As for either HR 623 (the low-flow toilet repeal bill) or the new ASME minimum performance standards, we will keep you apprised. HR 623 went nowhere in committee this summer, and new standards can be notoriously slow in development. The Checklist for Toilet Selection on page 5 will help to flush out what really matters when selecting a low-flow toilet. –

For more information:

John Wiedmann

Metropolitan Water District of

Southern California

700 N. Alameda Street

Los Angeles, CA 90012

213/217-6516, 213/217-7159 (fax)

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September 1, 2000