If "low-flow toilet" is on your search list, you're probably either (a) noticing your water bill, (b) trying to qualify for a state or municipal rebate, or (c) in a drought-zone where every gallon saved is a long-term hedge. Here's exactly what the numbers mean and how to choose between the three tiers.

The federal and state floors

Federal maximum since 1994: 1.6 GPF — the Energy Policy Act standard. Any new toilet sold legally in the US is at most 1.6 GPF.
EPA WaterSense voluntary spec: 1.28 GPF or lower, plus a flush-performance minimum (MaP-tested at 350g of solid waste). Roughly 70% of toilets at retail today carry the WaterSense label.
California state requirement (since 2014): all new toilets sold in CA must be 1.28 GPF or lower. Many manufacturers list "California compliant" on the box.
The ultra-low tier: 1.0 GPF (TOTO Aquia, some Kohler) and 0.8 GPF (Niagara Stealth Sabre) — the lowest gravity-fed flushing toilets certified by IAPMO and the EPA.

Will a low-flow toilet still flush properly?

This was a legitimate concern in the mid-1990s when manufacturers rushed 1.6 GPF designs to meet the federal mandate without redesigning the trapway. Multi-flush habits date from that era. It is no longer a concern in 2026. Modern 1.28 GPF and even 0.8 GPF toilets use re-engineered siphonic trapways, larger flush valves (3" or 3.5" instead of 2"), and pressure-assist or vacuum-assist systems to move waste with less water. The MaP (Maximum Performance) test independently verifies flush performance — look for a score of 800g or higher (the test measures how much simulated waste the toilet clears in a single flush).

The five low-flow models with rebate-eligibility track record

Niagara Stealth Sabre 0.8 GPF — UPC C22.303.01 — the lowest-flow gravity toilet on the market. Vacuum-assist trapway. EPA WaterSense Most Efficient list every year. Frequently rebate-eligible at $40–$100 per fixture in CA / TX / AZ utilities.
Niagara Liberty 1.28 GPF — UPC C11.101.01 R — the volume Niagara product. Lower price than the Sabre, still WaterSense.
TOTO Drake II 1.28 GPF — Double Cyclone flush. 1,000g MaP score. Top of the rebate-list for performance + water-saving balance.
Kohler Cimarron Comfort Height with AquaPiston flush — 1.28 GPF. Wide flapper, dual-action flush flush. Often runs $250–$350 at Home Depot.
American Standard Champion 4 with FloWise — 1.28 GPF. The largest 4" flush valve in residential. Strong choice for households with high paper use.

How to find your local rebate

The EPA WaterSense rebate finder (epa.gov/watersense/rebate-finder) is the single best aggregator — searchable by ZIP code. As of 2026, active rebates exist in 240+ US utility districts. Typical amounts:

California Bay Area utilities (EBMUD, SFPUC): $25–$200 per fixture
Los Angeles (LADWP): $40 per WaterSense toilet, $100 for ultra-low (0.8 GPF) models
Texas (San Antonio Water System, Austin Water): $50–$100
Arizona (SRP, Tucson Water): $50–$200
Florida (SFWMD, Tampa Bay): variable; usually capped at 2 toilets per household

Save your sales receipt and serial number — rebates require both. Submit within 60–90 days of purchase for most programs.