CSLB C-36 Plumbing ContractorFixture and Appliance InstallationMedium
A plumber is installing a water-saving toilet that features a dual-flush mechanism. The toilet has a full flush volume of 1.6 gallons per flush (GPF) and a reduced flush volume of 1.1 GPF. The client asks if this toilet is considered WaterSense compliant. To be WaterSense compliant, what is the maximum average flush volume allowed for a toilet?
- A1.28 GPF
- B1.6 GPF
- C2.0 GPF
- D1.0 GPF
Show answer & explanationAnswer & explanation
Correct answer: A. 1.28 GPF
Toilets must have a maximum average flush volume of 1.28 GPF to earn the WaterSense label. This is calculated as the average of two reduced flushes and one full flush. (2 * 1.1 GPF + 1.6 GPF) / 3 = (2.2 + 1.6) / 3 = 3.8 / 3 ≈ 1.267 GPF, which is less than 1.28 GPF, so this toilet is WaterSense compliant.
Why the other options are wrong
- B. 1.6 GPF was the federal standard for low-flow toilets before WaterSense, but is not WaterSense compliant on average.
- C. 2.0 GPF is considered a high-flow toilet and is not water-efficient by modern standards.
- D. 1.0 GPF is often seen in very low-flow models, but 1.28 GPF is the WaterSense standard.
WaterSense Toilet Flush Volume
To be WaterSense compliant, toilets must have a maximum average flush volume of 1.28 gallons per flush (GPF), calculated based on a weighted average of full and reduced flush cycles for dual-flush models.
- Maximum 1.28 GPF average.
- Includes dual-flush calculations.
- Saves significant water compared to 1.6 GPF.
Memory trick: WaterSense toilets flush with less, 1.28 is the best!