Low Flow Toilet Data: 1.6 vs 1.28 vs 0.8 Gallons, and What Each Saves

What counts as a low flow toilet in 2026: 1.6 gallons by law, 1.28 by market

The phrase low flow toilet started with the 1.6 gallon federal cap that took effect in 1994. That cap has not changed, but almost every model certified today flushes with 1.28 gallons or less, and a growing set goes down to 1.1, 1.0 and 0.8.

Federal law caps gravity tank, pressure-assist (flushometer tank) and electro-hydraulic toilets made after January 1, 1994 at 1.6 gallons per flush, and blowout toilets at 3.5 (42 U.S.C. 6295(k)). EPA's WaterSense label sets a lower ceiling of 1.28 gallons, which EPA describes as 20 percent below the federal standard (EPA).

High-efficiency toilet (HET): A toilet whose rated flush, or effective flush for a dual-flush model, is 1.28 gallons or less. Under WaterSense Version 1.2, a dual-flush toilet's effective volume is the average of two reduced flushes and one full flush (EPA WaterSense v1.2).

MaP score: The grams of soybean paste test media a toilet clears in one flush in the voluntary Maximum Performance test, up to a 1,000 gram ceiling (EPA performance overview, April 2022).

The rules by state, the federal history and toilet life spans are covered in our report on how long do toilets last; this report does not repeat that registry.

59.4% of 9,368 California-certified toilets sit exactly at the 1.28 gallon cap

The California Energy Commission database is the largest free, downloadable listing of toilets with a stated flush volume for every model. On November 8, 2026 it held 9,368 residential tank-type toilets, and none was rated above 1.28 gallons.

The CEC's Modernized Appliance Efficiency Database System listed 11,056 approved plumbing fixture records on November 8, 2026, of which 10,641 were toilets (CEC MAEDbS). After removing commercial flushometer valve, blowout, prison-type and vacuum toilets, 9,368 residential tank-type models remain.

• 5,563 models (59.4%) are rated at 1.28 gallons per flush, the California and WaterSense ceiling.
• 1,396 models (14.9%) fall between 1.11 and 1.27 gallons.
• 1,053 models (11.2%) are rated 1.01 to 1.10 gallons, including 240 at exactly 1.1.
• 1,160 models (12.4%) are rated 0.81 to 1.00 gallons, including 660 at exactly 1.0.
• 196 models (2.1%) are rated 0.80 gallons or less, including 180 at exactly 0.8.

Dual-flush toilets make up 3,543 of the 9,368 models, or 37.8%. The type of flush mechanism tracks the volume: 78.2% of gravity tank models sit at 1.28, while 51.2% of electro-hydraulic models and 54.1% of pressure-assist models are rated 1.10 gallons or less. The unweighted mean across all 9,368 models is 1.20 gallons per flush.

Models rated 1.10 gallons or less peaked at 43.8% of 2019 listings

Sorting the same 9,368 models by the date they were added shows lower volumes gaining ground after 2015, then settling. Because retired models drop out of the approved list, the early years are undercounted and the trend is indicative only.

Of models added in 2015 and still approved, 8.4% are rated 1.10 gallons or less. That share reached 43.8% for 2019 additions, 38.5% for 2022 and 37.0% for 2024, then fell to 27.0% in 2025 and 20.5% among the 2,545 models added so far in 2026 (CEC MAEDbS). The dual-flush share of 2026 additions is 41.5%.

One likely reason the lowest classes have not taken over: the CEC itself pulled back. A 2024 draft staff report proposed 1.1 gallons for single-flush toilets; the March 2026 request for information moved that to a long-term option after stakeholders raised drainline carry concerns (CEC TN 269259).

Do lower flush volumes clear less waste? 0.8 gallon models top out less often, but none scored under 600 grams

Every toilet sold in the US and Canada must clear 350 grams of test media in four of five flushes. MaP scores go further, up to 1,000 grams, and they show a clear pattern: lower volume models are less likely to hit the top score, yet all of them clear far more than the required load.

EPA set the 350 gram waste extraction load in the WaterSense specification, up from 250 grams in the earlier voluntary UNAR guideline, and the test is now part of the ASME A112.19.2/CSA B45.1 standard for all toilets (EPA, April 2022). In the CEC database, 9,265 of 9,368 models (98.9%) report exactly 350 grams, so that field shows a pass, not performance.

The MaP list of September 24, 2026 covers 6,616 tank-type and electro-hydraulic models, and 2,795 of them (42.2%) carry a numeric score (MaP Testing). Of the scored models, 2,105 (75.3%) cleared the 1,000 gram maximum. Only 2 scored below 350 grams, both at 300 grams and both in the 1.6 gallon class.

• 1.6 gallon models: 74.2% of 388 scored models reach 1,000 grams; 2.6% score under 500 grams.
• 1.28 gallon or unstated HETs: 79.3% of 2,104 scored models reach 1,000 grams; 0.5% score under 500 grams.
• 0.81 to 1.1 gallon models: 56.5% of 214 scored models reach 1,000 grams; none scores under 500 grams.
• 0.8 gallon models: 28.9% of 83 scored models reach 1,000 grams; 88.0% reach 800 grams; the lowest score is 600 grams.

The lowest 0.8 gallon score, 600 grams, is 1.71 times the 350 gram load every toilet must pass. MaP PREMIUM, a voluntary tier, requires both a single flush of 1.1 gallons or less and a score of at least 600 grams; 561 models on the September list carry the PREMIUM flag (MaP PREMIUM).

Clogging risk sits in the drain line more than in the bowl

A toilet can clear its bowl and still leave waste partway down a long or flat drain. That is the concern regulators and testers raise about the lowest flush volumes, and it applies most to older plumbing and commercial buildings.

EPA tested drainline carry for toilets flushing between 1.0 and 1.28 gallons on a 4-inch line at a 1 percent slope, with no shower or washer water to help, and reports that every model met its criteria (EPA, April 2022). Those tests did not cover 0.8 gallon models.

The MaP PREMIUM list cautions that its toilets are recommended for homes or light commercial sites where other fixtures add enough flow to the drain line (MaP PREMIUM list, September 2026). In California, stakeholders cited drainline carry in commercial settings and existing residential plumbing when the CEC weighed a 1.1 gallon standard, and said a 0.8 gallon reduced flush may be closer to best available technology than a broad minimum (CEC TN 269259).

Homes with older drain materials face their own issues regardless of flush volume; see our reports on cast iron pipes and Orangeburg pipe.

A 3.5 to 1.28 gallon swap saves a 2.49 person household 10,088 gallons a year

Savings depend on three numbers: how often people flush, how many people live in the home, and the gallons cut per flush. Using measured flushing rates and current Census household size, the old toilet you replace matters far more than how low the new one goes.

The Water Research Foundation's REU2016 study measured 5.0 flushes per person per day in single-family homes at 23 study sites, unchanged since 1999, with an average flush of 2.6 gallons, down from 3.65 (WRF REU2016). The 2025 American Community Survey puts the average US household at 2.49 people (Census ACS B25010).

At the 24-city median price of $17.69 per 1,000 gallons, replacing a 3.5 gallon toilet with a 1.28 gallon model saves 10,088 gallons and $178.41 a year; going to 0.8 gallons instead saves 12,269 gallons and $216.99. Replacing a 1.6 gallon toilet saves 1,454 gallons and $25.72 at 1.28, or 3,635 gallons and $64.29 at 0.8. A home whose toilets flush at the REU2016 average of 2.6 gallons saves 5,998 gallons and $106.08 by moving to 1.28.

EPA's own estimate is nearly 13,000 gallons and $170 a year for an average family, while its statistics page gives $130 (EPA; EPA statistics). Our estimate for a 3.5 gallon baseline is 2,912 gallons lower than EPA's, likely because EPA's figure allows for older toilets at up to 6 gallons per flush; EPA does not publish its household size on the page.

The same toilet swap is worth $88.79 a year in Jacksonville and $366.45 in San Francisco

Water and sewer prices, not water saved, drive most of the gap between cities. San Francisco households are smaller than Jacksonville's, yet they save 4.1 times as much money because each 1,000 gallons costs $43.07 there and $9.17 in Jacksonville.

We applied the formula to each of the 24 large cities with complete water and sewer rates in our average water bill report, using each city's 2025 ACS household size. Replacing a 3.5 gallon toilet with 1.28 saves more than $200 a year in 7 cities, with a 24-city median of $155.19.

A toilet swap is often part of a larger bathroom project; our bathroom remodel cost guide and tub-to-shower conversion cost guide cover those budgets. For how toilets fit into total household use, see average water usage per person and how much water a shower uses.

Replacing a working 1.6 gallon toilet saves $12.80 to $52.82 a year

For the many homes that already have 1.6 gallon toilets from the 1990s and 2000s, the water case for replacement is thin. The yearly savings in most big cities are smaller than a single plumber visit.

Moving from 1.6 to 1.28 gallons saves a household $12.80 a year in Jacksonville and $52.82 in San Francisco, with a 24-city median of $22.37; 10 of the 24 cities come in under $20. Going further, from 1.28 to 0.8 gallons, adds a median $33.55 a year.

1.6 gallon toilets remain legal under federal law, which has not changed since 1994 (42 U.S.C. 6295(k)). ASAP counts 12 states plus DC with stricter rules (ASAP, July 2024); where a new 1.6 gallon toilet can still be sold is tracked in our how long do toilets last report.

Dual flush toilets save less than rated because people pick the half flush 1.28 times per full flush, not 4

WaterSense rates a dual-flush toilet as if it is used two reduced flushes to one full flush. Field studies cited by the CEC found far fewer reduced flushes, which pushes real average use up.

The CEC reports an observed ratio of 1.28 reduced flushes per full flush across six field studies from 2000 to 2011, against a theoretical 4 if every liquid-only trip used the reduced button (CEC TN 269259). At that observed ratio, a 1.28/0.8 toilet averages 1.011 gallons per flush instead of the rated 0.96, and a 1.6/1.1 toilet averages 1.319, above the 1.28 cap it is rated under at 1.267.

EPA's WaterSense Version 2.0 would drop the effective volume formula and cap the full flush itself at 1.28 gallons, but EPA has paused its effective date and Version 1.2 remains in force (EPA). The CEC is weighing the same change for California, with a 0.9 gallon reduced flush cap.

Where each number comes from, and the two databases we could not open

Certification counts come from the CEC export; flush scores from the MaP list; savings from REU2016, ACS 2025 and KBR's October 2026 rate table. Two federal and EPA listings with national flush volumes were not reachable without workarounds, so they are not used.

The CEC export was taken from the public Advanced Search on November 8, 2026 (Plumbing Fixtures, Approved). The MaP complete list is the September 24, 2026 edition. The US Department of Energy certification database returned HTTP 403 to our request, and EPA's WaterSense product download is served through a keyed API, so neither was used; the reasons are logged in excluded.md.

This report is a data summary, not plumbing advice. Drain condition, line length and slope matter for any toilet, and a licensed plumber can assess a specific home.

Ratios behind the comparison

Download the calculations (CSV)

Where the numbers diverge

1. The CEC database listed 9,368 approved residential tank-type toilets on November 8, 2026, none above 1.28 gallons per flush.^[1]
2. 5,563 of those models (59.4%) are rated at exactly the 1.28 gallon cap.^[1]
3. 2,409 models (25.7%) are rated 1.10 gallons or less and 1,356 (14.5%) are rated 1.00 or less.^[1]
4. Dual-flush models account for 3,543 of 9,368 certified toilets (37.8%).^[1]
5. 51.2% of electro-hydraulic and 54.1% of pressure-assist models are rated 1.10 gallons or less, against 15.4% of gravity tank models.^[1]
6. Models rated 1.10 gallons or less were 43.8% of 2019 additions still approved in 2026 and 20.5% of 2026 additions to date.^[1]
7. Of 2,795 scored models on MaP's September 24, 2026 list, 2,105 (75.3%) cleared the 1,000 gram maximum.^[2]
8. 28.9% of 83 scored 0.8 gallon models reached 1,000 grams, against 74.2% of 388 scored 1.6 gallon models.^[2]
9. No scored model at 1.1 gallons or less scored under 500 grams; 2.6% of 1.6 gallon models did.^[2]
10. REU2016 measured 5.0 toilet flushes per person per day and an average flush of 2.6 gallons in US and Canadian single-family homes.^[10]
11. Replacing a 3.5 gallon toilet with 1.28 saves a 2.49 person US household 10,088 gallons a year, or $178.41 at the 24-city median rate of $17.69 per 1,000 gallons.^[10][11][12]
12. Across 24 large cities, that swap saves $88.79 a year in Jacksonville and $366.45 in San Francisco.^[10][11][12]
13. Replacing a 1.6 gallon toilet with 1.28 saves a 24-city median of $22.37 a year.^[10][11][12]
14. Dual-flush users chose the reduced flush 1.28 times per full flush in six field studies from 2000 to 2011, not the theoretical 4.^[14]

Summary

• None of 9,368 residential tank-type toilets certified in California on November 8, 2026 is rated above 1.28 gallons; 59.4% sit exactly at 1.28.
• 2,409 models (25.7%) are rated 1.10 gallons or less, and 196 (2.1%) are rated 0.80 or less.
• Dual-flush designs make up 37.8% of certified models.
• On the September 2026 MaP list, 28.9% of scored 0.8 gallon models clear 1,000 grams versus 74.2% of 1.6 gallon models, but every 0.8 gallon model scored at least 600 grams, 1.71 times the 350 gram requirement.
• Replacing a 3.5 gallon toilet with 1.28 saves a 2.49 person household 10,088 gallons and $178.41 a year at the 24-city median rate.
• The same swap is worth $88.79 a year in Jacksonville and $366.45 in San Francisco, a 4.1 times gap driven by water and sewer prices.
• Replacing a working 1.6 gallon toilet saves only $12.80 to $52.82 a year across 24 cities.
• At observed use, dual-flush toilets average more water than rated: a 1.6/1.1 model averages 1.319 gallons, not 1.267.

Frequently asked questions

Related guides, services and research

• Small bathroom remodel cost
• Tub to shower conversion cost
• Water Damage Statistics: Household Leaks, Mold and Insurance Claims
• Water Heater Temperature: 120 vs 140 Degrees, Scalds and the Rules
• What Size Water Heater Do I Need? First-Hour Ratings vs Household Size
• When Was Asbestos Banned? Every Federal Action on Home Building Products
• All kitchen and bath research

Reproduce this analysis

Every figure comes from the files below. The scripts that pulled and computed them are kept with the report and can be re-run.

Data quality and exclusions

• MAEDbS CSV: 16 records were split across two lines by line breaks inside model numbers; they were re-joined, giving 11,056 records, matching the 11,056 the search page reported.
• MAEDbS: 1,688 non-residential records removed (urinals and flushometer valve, blowout, prison-type and vacuum toilets), leaving 9,368 residential tank-type toilets; 0 had a missing flush volume.
• MAEDbS: the Waste Extraction Value field reads exactly 350 grams for 9,265 of 9,368 models (98.9%), so it was not used as a performance measure.
• MaP list: 24 legend rows without a model number were dropped, leaving 6,616 models; 3,821 unscored models were excluded from score statistics.
• MaP list: 57 models carry a WaterSense flag but no HET flag; they were excluded from flush class comparisons because WaterSense requires 1.28 gallons or less.
• MaP list: flush volumes below 1.28 were taken from MaP's own notes in model text for 432 models (104 at 0.8 or less, 328 at 0.81 to 1.0, plus 13 at 1.01 to 1.1); untagged HETs were grouped with 1.28.

Methodology

Source selection: we used the California Energy Commission's MAEDbS because it is the largest free listing that gives a rated flush volume for every certified toilet, and the MaP Testing complete list because it is the only public source of measured maximum flush performance by model. Savings inputs come from the Water Research Foundation's REU2016 study (flushes per person), the Census ACS 2025 1-year Table B25010 (household size) and the October 2026 water and sewer rate table in our average water bill report.

Inclusion and exclusion: from 11,056 MAEDbS plumbing fixture records we kept 9,368 residential tank-type toilets (gravity tank, dual-flush, electromechanical hydraulic and flushometer tank), dropping urinals, flushometer valve, blowout, prison-type and vacuum toilets. From the MaP list we dropped 24 legend rows and set aside 57 models whose WaterSense flag conflicts with a missing HET flag.

Conflicting numbers: EPA states toilets use nearly 30 percent of indoor water on its web page and nearly 25 percent in its May 2024 fact sheet, and $170 versus $130 a year in savings on two pages; both are shown. REU2016's measured 2.6 gallon average flush is used as a separate baseline rather than blended with the 3.5 and 1.6 gallon scenarios.

Derived metrics: volume shares are model counts divided by 9,368. MaP class shares are counts of models at each score divided by scored models in the class. Savings use gallons = 5.0 x persons x 365 x (old minus new gallons per flush) and dollars = gallons / 1,000 x the next-1,000-gallon water plus sewer price at 6,000 gallons a month. Dual-flush observed volume = (full + 1.28 x reduced) / 2.28. All calculations are in scripts/ and derived_metrics.csv.

Limitations: model counts are listings, not sales or installed stock. MaP volume classes below 1.28 depend on MaP's free-text notes. Savings assume every at-home flush goes through the replaced toilet(s).

Last updated 2026-11-08. Not plumbing, legal or financial advice.

This report presents published data with its limitations. It is not legal, financial or investment advice.

Sources, ranked by quality

Tier 1: primary and official sources (11)

• [1] California Energy Commission. Modernized Appliance Efficiency Database System (MAEDbS), Plumbing Fixtures, Approved models, CSV export. Approved listings as exported 2026-11-08. Accessed 2026-11-08.
• [5] U.S. Environmental Protection Agency. WaterSense: Residential Toilets. Current page. Accessed 2026-11-08.
• [6] U.S. Environmental Protection Agency. WaterSense Specification for Tank-Type Toilets, Version 1.2. Effective 2014-06-02. Accessed 2026-11-08.
• [7] U.S. Environmental Protection Agency. WaterSense Performance Overview: Tank-Type Toilets. April 2022. Accessed 2026-11-08.
• [8] U.S. Environmental Protection Agency. WaterSense Labeled Toilets fact sheet (832-F-24-008). May 2024. Accessed 2026-11-08.
• [9] U.S. Environmental Protection Agency. WaterSense: Statistics and Facts. Current page. Accessed 2026-11-08.
• [10] Water Research Foundation. Residential End Uses of Water, Version 2: Executive Report (REU2016), Internet Archive copy of the WRF PDF. Published 2016; logging mostly 2010 to 2013. Accessed 2026-11-08.
• [11] U.S. Census Bureau. American Community Survey 2025 1-year, Table B25010 Average Household Size of Occupied Housing Units by Tenure. 2025. Accessed 2026-11-08.
• [13] U.S. Government Publishing Office (govinfo). 42 U.S.C. 6295(k), Standards for water closets and urinals (United States Code, 2023 edition). In force since 1994. Accessed 2026-11-08.
• [14] California Energy Commission. Request for Information: Appliance Efficiency Regulations for Water Closets, Docket 22-AAER-05, TN 269259. Docketed 2026-03-20. Accessed 2026-11-08.
• [15] U.S. Environmental Protection Agency. WaterSense Specification for Tank-Type Toilets, Version 2.0. May 2024; effective date paused. Accessed 2026-11-08.

Tier 2: trade bodies, market research, company data (6)

• [2] MaP Testing (Veritec Consulting and Koeller and Company). Maximum Performance (MaP) of Tank-Type and Electro-Hydraulic Toilet Models, complete list (XLSX). List dated 2026-09-24. Accessed 2026-11-08.
• [3] MaP Testing. Toilet and Urinal List Downloads. Page dated 2026-09-25. Accessed 2026-11-08.
• [4] MaP Testing. MaP PREMIUM. Page last updated 2026-06-25. Accessed 2026-11-08.
• [12] Kitchen and Bath Renovators. Average Water Bill in the 30 Largest US Cities, table t3: price of the next 1,000 gallons (CSV). Rates in effect for an October 2026 bill. Accessed 2026-11-08.
• [16] Appliance Standards Awareness Project (ASAP). Water Efficiency Standards for Toilets, fact sheet. July 2024. Accessed 2026-11-08.
• [17] MaP Testing. MaP PREMIUM tank-type and electro-hydraulic toilet list (PDF). List dated 2026-09-09. Accessed 2026-11-08.