Extensive testing on 49 of the most popular toilets in the United States resulted in a performance report by the NAHB Research Center in cooperation with Seattle Public Utilities and the East Bay Municipal Utility District (EBMUD) of Oakland, Calif.

The objective of the report "Summary Test Report: Water Closet Performance Testing" was to develop information on product performance, water savings reliability and physical characteristics that will assist consumers in evaluating products and making purchase choices.

With flushing toilets using the largest amount of water in U.S. homes -- nearly 18 gallons of water a day per person -- many utilities are encouraging customers to replace older models with water-efficient toilets. However, the study found not all water-efficient toilets have the same flushing performance.

Flushing performance, flush volume, trap diameter, water spot area and other characteristics of each toilet were determined by Research Center technicians using various methods.

While most of the tested fixtures were 1.6-gpf, a few had design volumes significantly less than the standard. Testing included gravity, pressure-assist and vacuum-assisted models, as well as a few special models, such as dual-flush, flapperless, and air-assist units.

A Flush Performance Index (FPI), used as a general indication of expected performance, was calculated based on how much material (floating and sinking sponges) remained in the bowl after flushing.

David Broustis, a conservation specialist with Seattle Public Utilities, said, "This research provides a resource to educate consumers on the well-performing products to choose from when selecting a water-efficient toilet."

To download the study report, including a summary of the testing results, visit www.nahbrc.org or www.toolbase.org. For more information, call the NAHB Research Center's Toolbase Hotline at 800/898-2842.