Short definition
1.6 gallons per flush (gpf) is the federal maximum for new residential toilets, set by the Energy Policy Act of 1992 and effective since 1994. 1.28 gpf is the EPA WaterSense efficiency label for high-efficiency toilets (HETs) — about 20% less water per flush. Several WA utilities offer rebates of $50 to $100 for upgrading from a pre-1994 toilet to a WaterSense-labeled 1.28 gpf model.
What it is
Three flush-volume tiers cover the residential market:
- 3.5 gpf or higher (pre-1994). The pre-EPAct standard. Common in pre-1995 WA homes that haven’t been remodeled.
- 1.6 gpf (federal cap, current). Required since 1994 for new manufacture. The default for most non-WaterSense toilets sold today.
- 1.28 gpf (WaterSense / “HET”). EPA-certified high-efficiency. Must also pass MaP (Maximum Performance) testing — typically 600 grams of solid waste per flush — to verify the lower volume still flushes properly.
- Dual-flush 1.28/0.8 gpf. Full flush at 1.28; reduced (liquid-only) flush at 0.8. Average mixed use lands around 1.0 gpf.
The federal 1.6 gpf cap is mandatory; the 1.28 gpf WaterSense rating is a voluntary efficiency label used by utility rebates. WA does not mandate 1.28 gpf statewide (some states do — California, Colorado, New York for new construction), but Saving Water Partnership utilities incentivize it.
Why it matters to a homeowner
If your home was built before 1995 and the toilet hasn’t been replaced, you’re flushing 3.5 to 5 gallons per flush — easily double a modern WaterSense toilet. EPA estimates an upgrade from a 3.5 gpf to a 1.28 gpf toilet saves about 13,000 gallons per year for an average household.
The economic case in WA: a WaterSense toilet runs $150 to $600 (most popular models around $250 to $400). Saving Water Partnership offers $100 toward a WaterSense replacement of a pre-2011 toilet. Washington Water (Tacoma area) offers $50 for MaP-600 models. Combined with the water savings, an upgrade often pays back inside three to five years.
The “low-flow toilets don’t flush well” complaint is mostly from early 1990s 1.6 gpf models that hadn’t refined their bowl design. Modern 1.28 gpf toilets that pass MaP-600 testing flush as well as any 3.5 gpf toilet ever did.
Common variants
- 1.6 gpf (federal max).
- 1.28 gpf (WaterSense HET).
- 0.8 gpf (UHET — ultra-high-efficiency). Less common; some commercial.
- Dual-flush 1.28/0.8 gpf. Two-button valve.
Washington note
WA defaults to the federal 1.6 gpf cap; there’s no state mandate for 1.28 gpf. The Saving Water Partnership — which includes Seattle, Tacoma, Bellevue, Everett, Cascade Water Alliance, and most regional utilities — runs an active toilet rebate program. As of 2026 the standard is $100 toward replacing a pre-2011 toilet with a WaterSense-labeled model. Washington Water (Pierce County) offers $50 for MaP-600 toilets. Other WA utilities (Spokane, Vancouver, etc.) have run similar programs intermittently — verify your utility’s current rebate page before purchase. Confirm the rebate amount with the utility directly before publishing this number on the site, as program funding varies year to year.