High Efficiency Toilets

High efficiency toilets accomplish the same waste removal as standard models, but use significantly less water. Prior to 1992, standard toilets used between 3.5 and 7 gallons of water per flush (gpf). Since 1992, all toilets sold in the United States have been required by code to use less than 1.6 gpf, following the Ultra-Low Flush standard (ULFT). In 1998, the industry developed a new voluntary high-efficiency standard, the high-efficiency toilet, or HET. To meet this standard, HETs are required to use a maximum of 1.28 gpf—20% less water than the code maximum of 1.6 gpf. Some HET models are now available that use even less water. Some use less than 1.0 gpf. In addition, many dual-flush models are now available. These toilets use two different volumes of water, depending on the type of waste, to increase efficiency.

General Recommendations
When choosing a toilet, one should consider availability, quality, price, and aesthetics. Low-flow HET's and dual flush toilets are increasingly available, reliable, and are dropping in price. Toilets range in performance. Higher water-consumption models do not always work better than more efficient models. Once installed, a toilet's water use is fixed for many years, often decades. Therefore, the most efficient, well-functioning model should be used. The WaterSense program of the US EPA maintains a list of toilets that meet their high efficiency standards. Care should be taken to install dual flush toilets in locations that will deliver full water savings potential. Click here for more information on installing dual flush toilets.

The EPA estimates that by 2013, 36 states will face water shortages.1 Toilets are some of the most water consuming devices found in the home. Using a high-efficiency toilet can significantly reduce water consumption, lessening the burden on water tables and municipal water systems.

Notes on Use
As the volume of water used to clear a toilet's bowl continues to decrease, concerns are mounting that there may not be adequate water to transport solid waste to the sewer. To assess these concerns, the California Urban Water Conservation Council conducted a series of laboratory tests in 2005. Using a variety of HET fixtures and MaP (a toilet performance rating) testing materials, the council found that, in all cases, there was sufficient water to move the waste through a typical residential drain line to the sewer, provided that the drain line was properly designed and installed. These tests convinced the EPA that HETs should qualify for the WaterSense program.2

However, in the case of degraded drain lines (sagging pipes, pre-existing build-up, root intrusion, broken pipes, extremely long drain lines, etc.), the council urges caution when recommending HETs. Although any toilet may have trouble clearing waste to the sewer in these conditions, HETs may be more susceptible because of reduced water volume. To date, there is no public data available to confirm or deny this notion.3

Options and Analysis

Toilet Types
On average, HETs outperform ULFTs in terms of flushing power and performance, even while using 20% to 40% less water. In 2006, the California Urban Water Conservation Council found that ULFTs use 1.6 gpf to remove an average 450 grams of solid waste, while HETs use 1.28 gpf or less to remove an average 550 grams. HET's better performance most likely results from increased levels of testing and engineering that contribute to the development of high efficiency toilets.

Both ULFTs and HETs use a variety of technologies to achieve flushing power. There are three basic types: standard gravity assist models that rely on the weight and movement of water, pressure assisted models that use a pressurized water tank to move water with a higher velocity, and vacuum assist models that combine a standard gravity flush with vacuum-induced suction in the toilet trap below the bowl. Dual flush technology is an additional development that allows users to choose between a solid waste mode with standard 1.6 gallons per flush and a liquid waste mode with reduced water requirements. This technology can be combined with any of the three toilet types mentioned above to achieve the HET standard. Each of the above strategies is outlined in greater detail here.

Toilet Ratings
There are currently two primary standards for the manufacture of toilets in the United States: the EPA act guidelines for water use (no more that 1.6 gallons per flush) and the EPA WaterSense certification (for toilets that use less than 1.28 gallons per flush, on average). Some dual flush toilets that have a large flush with a volume greater than 1.28 gallons may still qualify for the HET rating, as their estimated average performance is better than 1.28 gpf.

When the federal government mandated ULFTs in 1994, many manufacturers were caught with models that had not been adequately engineered or tested. This resulted in many low-performing models and consumer backlash. With the worst performing models, water usage may have actually increased because two or more flushes were required to clear the bowl. Since then, most manufacturers have demonstrated the capability to meet ULFT standards with many well-performing models.

In contrast, HETs have been in steady development and testing for almost ten years, resulting in many models that outperform ULFTs in standardized tests while using up to 40% less water. HETs that meet the 1.28 gallon per flush standard, in addition to ASME performance standards, qualify for the EPA's WaterSense program.

Water Consumption and Cost

gallons per flush (gpf) water use per year (gal) water savings* (gal) water cost per year water cost over 10 yrs water cost savings over 10 years*
5.0 19,055 -12,957 $119.86 $925.50 -$629.34
1.6 6,098 0 $38.35 $296.16 $0
1.28 4,878 1,220 $30.68 $236.93 $59.23
1.0 3,811 2,287 $23.97 $185.10 $111.06
0.8 3,049 3,049 $19.18 $148.08 $148.08

* In comparison to the 1.6 gpf toilet.

In homes where older toilets are still in place, the water savings of a newer 1.6 gpf (or better) toilet is a cost-effective choice. The amount saved in water consumption easily compensates for the cost of a new toilet in just a couple years. When choosing a new toilet to install, consider the long-term water costs and potential savings. In addition to environmental benefits, long-term water cost savings often completely offset the cost premium of more water efficient models.

High efficiency toilets are increasingly available at local supply shops, through mail order, and through nationwide retailers. Almost all major toilet manufacturers now offer HETs in a variety of styles and options.

Future Recycling & Waste Generation
Toilets are mainly composed of porcelain and, if recycled, can be ground into roadway base or other aggregate or gravel. Though it does divert waste from landfills, this process is energy intensive.

Other Resources

1 "Why Water Efficiency?" WaterSense Web site. 10 Jul. 2008. U.S. Environmental Protection Agency. 28 Jul 2008. www.epa.gov/WaterSense/water/why.htm.
2 "High Efficiency Toilet Questions." WaterSense Web site. 28 Mar. 2008. U.S. Environmental Protection Agency. 28 Jul 2008. www.epa.gov/watersense/fq/fq_toilets.htm.
3 "High Efficiency Toilet Questions." WaterSense Web site. 28 Mar. 2008. U.S. Environmental Protection Agency. 28 Jul 2008. www.epa.gov/watersense/fq/fq_toilets.htm. and Koeller, John. "A Primer on HETs." California Urban Water Conservation Council. 1 Feb. 2007. 28 Jul 2008. www.cuwcc.org/toilet_fixtures/Primer_On_HETS_07-02-01.pdf.