High-efficiency toilet

Short definition

A high-efficiency toilet (HET) uses 1.28 gallons per flush or less — about 20% less than the federal 1.6-gpf standard. EPA WaterSense-labeled HETs must also pass a flush-performance test, so they don’t sacrifice function for water savings. In WA, several utility programs offer rebates for replacing pre-2004 toilets with rebate-qualifying HETs.

What it is

The federal max for new toilets has been 1.6 gallons per flush since the Energy Policy Act of 1992. The EPA WaterSense program goes further: WaterSense-labeled toilets use ≤1.28 gpf and must pass the MaP (Maximum Performance) flushing test, which measures how reliably they clear solid waste. The current WaterSense Tank-Type Toilet Specification (Version 2.0, effective July 1, 2025) requires a MaP score of at least 350 grams of soybean paste in a single flush.

Sub-categories:

• Standard HET — 1.28 gpf, single-flush.
• Dual-flush HET — typically 0.8 gpf liquid + 1.28 gpf solid; better real-world savings.
• Ultra-low-flush — 1.0 gpf; some utility programs reward these higher.
• Pressure-assist HET — uses internal compressed air to flush; works well in homes with low household pressure.

For rebate eligibility, look for the WaterSense label and a MaP score of at least 800 grams (sometimes called “MaP Premium”).

Why it matters to a homeowner

Toilets are the single biggest indoor water use in most WA households — typically 24–30% of indoor consumption. Swapping a pre-1994 toilet (3.5 gpf) for an HET cuts about 60% of that. Even replacing a 1.6-gpf model from 1995–2003 saves 20%. With a $100 rebate plus a $200–$350 toilet, the install often pays back inside two years on water savings alone.

When a plumber says “WaterSense compliant” or “MaP-rated,” they’re describing exactly the spec needed for rebate eligibility. If you’re paying for a rebate-qualifying install, the plumber should be able to point to the WaterSense label and the MaP score on the spec sheet.

A few caveats:

• Rough-in fit — Pre-1970 WA homes (especially craftsman bathrooms in Ballard, Wallingford, Tacoma) often have non-standard 10-inch or 14-inch rough-ins. Confirm before ordering.
• Settled floor — Use a wax-free seal instead of wax for floors that aren’t level.
• Cheap models with undersized trapways flush poorly. Pick a MaP-rated model rather than the cheapest WaterSense badge.

Common failure modes (post-install)

• Weak flush from undersized trapway — pick a MaP-rated ≥800 g model.
• Rim-jet mineral buildup — Spokane and Eastside hard-water; vinegar descale.
• Flapper hardens in 5–7 years — same lifespan as older toilets, sometimes faster on softer-rubber HET flappers.
• Improper rough-in fit on retrofits — measure twice before ordering.

Washington note

Several WA utility programs offer toilet-replacement rebates. Programs change year to year; verify the amount and current eligibility before purchasing.

• Saving Water Partnership (SPU plus member utilities — Bellevue, Redmond, Seattle metro): typically up to $100 per toilet, maximum two per household, replacing pre-2004 or pre-2011 toilets depending on category. Toilet must be WaterSense-labeled at MaP Premium and meet the program’s gpf threshold.
• Free toilet program for income-qualified Seattle homeowners — Seattle Public Utilities runs this directly; income thresholds and program window change annually.
• Whatcom Water Alliance / City of Bellingham: typically $100 per toilet.
• Cascade Water Alliance member utilities: similar amounts; terms vary by member utility.
• Tacoma Water: separate program from Saving Water Partnership; verify current 2026 amount directly.

A common WA scenario: a pre-1994 Seattle bungalow with the original 3.5-gpf toilet. Swap to a $300 WaterSense HET, claim the $100 rebate, and the net cost is about a year’s water savings on that fixture alone. Multi-bathroom homes prioritize the most-used toilet first, since the rebate caps at two per household in most programs.

Common variants

• HET (≤1.28 gpf) vs. standard low-flow (1.6 gpf federal min) vs. ultra-low-flush (1.0 gpf).
• Single-flush vs. dual-flush HET — dual gives more real-world savings.
• Gravity-fed vs. pressure-assist — pressure-assist works better at low household pressure.
• HET vs. composting toilet — composting is off-grid only and isn’t rebate-eligible.