The amount of water used by a flush toilet is used as a measure of its efficiency.


Volume per Flush


3.5 to 5.0 gallons

low efficiency or high flow

single flush, 1.6 gallons

low flow or ultra low flow (ULF)

<= 1.28 gallons

high efficiency toilet (HET)

dual flush, < 1.0 gallons and <= 1.6 gallons

high efficiency toilet (HET)



• A dual flush toilet has a low volume setting for urine and a higher volume for feces. The average water use per day is in the high-efficiency range.


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