What Is a Dual Flush Toilet?

Function

• Dual flush toilets offer two flush modes: a low water flush for disposing of liquid waste only, and a higher volume flush for dealing with solid waste. Most residential dual-flush toilets have buttons on top of the water tank to control which type of flush they produce. Commercial toilets have a handle that, when pulled upward, produces a low volume flush, and when pulled downward, produces a normal flush.

Volume

• Modern dual flush toilets use 1.28 to 1.6 gallons of water per high volume flush, the current EPA standards for efficient toilets. The low volume flush mode saves about a half-gallon per toilet flush, which can add up over time. According to the American Solar Energy Society, most people use the lower volume mode four times as often as the higher volume flush. If users choose the correct mode each time, they could save about 30 percent of toilet water.

Considerations

• Dual flush toilets require users to choose the right flush mode each time they use the toilet. When users aren't familiar with this type of toilet, they may simply choose a normal flush, reducing or eliminating water savings. Many commercial dual flush toilet installations have signage on or near the toilet to tell users how to operate them. Some toilets also have a special green handle to differentiate them from conventional toilets and encourage users to choose the correct flush mode.

Effectiveness

• In a study published in the American Solar Energy Society's SOLAR 2010 Conference proceedings, 98 percent of surveyed building occupants were aware of their building's flush toilets. However, only 55 percent of these people used the small flush option regularly. Ten percent used it infrequently or never. Even with thus reduced use, however, toilets in the study building still saved 32 percent more water when compared to conventional toilet use.