Older toilets typically use 3.5 gallons of water per flush (gpf) or more. Standard new toilets use 1.6 gpf. Toilets that use an average of 1.28 gpf or less are called High Efficiency Toilets (HETs) and are now required by the state's building code in all new homes in California.
HETs are available in dual-flush, pressure-assist and conventional gravity-flush models. Dual-flush toilets have two buttons: one for a half flush and the other for a full flush. The average gallons per flush of dual-flush toilets is based on the average of one full flush and two half-flushes. In the past, some models of low-flow toilets didn't work well, but the majority of today's High Efficiency Toilets perform well and don't require multiple flushes.
To give buyers confidence that their products won't require double flushing or get plugged up regularly, many manufacturers take part in the Maximum Performance (MaP) Testing Program. This voluntary program provides flushing performance scores for more than 2,200 toilets. For information about MaP testing for toilets, go to www.map-testing.com.
The Green Product Directory features a selection of WaterSense–labeled High Efficiency Toilets that have been independently verified to perform well. Each of these toilets has a flush volume of no more than 1.28 gallons per flush* and has a MaP score of at least 600. Many manufacturers regularly introduce new models of High Efficiency Toilets, so think of this list as a starting place when shopping for a new toilet.
*To figure the average flush volume of a dual-flush toilet, multiply the partial-flush gpf by two, add the full flush volume and divide the sum by three. So if the partial-flush volume is 1.1 gpf and the full-flush volume is 1.6 gpf, the average flush volume = (2x1.1)+1.6 = 3.8/3 = 1.27 gpf