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Toilet Wastewater Savings

In many places you are charged for wastewater based on the amount of water used. In some areas, wastewater charges are higher than water rates! Replacing your old toilet can save water and wastewater. All water savings achieved by your new toilets will result in identical wastewater savings.

A recent study conducted in Seattle measured water use in single-family homes before and after installation of high efficiency toilets (DeOreo, et. al. 2001). About half of the toilets installed were standard 1.6 gallon per flush (gpf) models. The other half were dual flush toilets that offer a 0.8 gallon flush for liquid and a 1.6 gallon flush for solids. The results are shown below in Table 1.

Table 1: Wastewater use in homes with standard, 1.6 gallon, and dual flush toilets

Avg. Gallons per Flush
Avg. Gallons per Person Per Day
Non-conserving Home
Conserving home (1.6 gpf toilet)
Conserving home (dual flush toilet)

What happens when a family of four replaces all their toilets with new high efficiency models. Figure 1 shows a projection of the difference in wastewater volumes for the standard non-conserving toilet, 1.6 gpf model, and dual flush model. The family would reduce wastewater volume by more than 14,000 gallons of water per year by installing 1.6 gpf toilets and more than 17,000 gallons of wastewater per year by installing dual flush toilets!

Figure 1: Annual toilet wastewater usage with different fixtures.

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