Water Efficiency and Conservation
What this domain covers
The water efficiency domain tests whether you can convert fixture and system performance into measured water savings, and whether you know which limits come from federal law, which from plumbing code, and which from a voluntary label. Expect questions on fixture flow rates, pressure control, metering and leak detection, and on-site alternate sources such as greywater and rainwater.
Core rules
- Federal baselines come from EPAct 1992: 1.6 gpf water closets, 1.0 gpf urinals, 2.2 gpm lavatory faucets at 60 psi, 2.5 gpm showerheads at 80 psi.
- WaterSense is stricter and voluntary: 1.28 gpf toilets, 0.5 gpf urinals, 1.5 gpm residential lavatory faucets (0.5 gpm in public settings), 2.0 gpm showerheads.
- Dual-flush closets are rated on effective flush volume, averaged over one full flush and three reduced flushes, and must not exceed 1.28 gallons.
- Where supply pressure exceeds 80 psi, a pressure-reducing valve is required; excess pressure wastes water and shortens fixture life.
- The Uniform Plumbing Code addresses greywater in Chapter 16 and rainwater catchment in Chapter 17; both require signage, dual piping, and backflow protection.
- Cooling towers save water by running at higher cycles of concentration, controlled by conductivity rather than by timer.
Worked example
A 200-room hotel with 3.5 gpf closets, six flushes per room per day, replaces them with 1.28 gpf models. Savings per flush = 3.5 − 1.28 = 2.22 gal. Annual savings = 2.22 × 6 × 200 × 365 = 972,360 gallons, just under one million gallons, before any sewer or energy benefit is counted.
Traps
Confusing gpf with gpm; assuming a WaterSense label is required by code when it is voluntary and simply exceeds code; ignoring pressure and leak losses when projecting retrofit savings; treating greywater and municipal reclaimed water as interchangeable, when they follow different code paths and different treatment requirements.