High Efficiency Toilets Explained (HET)

High efficiency toilet, almost always shortened to HET, is the industry term for a toilet that uses no more than 1.28 gallons of water per flush. That number is not arbitrary. It sits exactly 20 percent below the 1.6-gallon-per-flush ceiling that federal law has required on every new toilet sold in the United States since 1994, and 20 percent is the threshold the EPA chose for its WaterSense efficiency label. So in practice, "high efficiency toilet" and "1.28 GPF toilet" describe the same class of fixture, and the strongest members of that class also carry the blue WaterSense badge. The label is the certification, HET is the category, and 1.28 gallons is the number that defines both.

The word "efficiency" matters because it implies more than just using less water. A toilet that used 1.0 gallon but failed to clear the bowl would not be efficient at all, since a second flush would push real-world water use back above a 1.6-gallon model. True efficiency means doing the same job, clearing waste fully, with less water. That is why every serious high efficiency toilet pairs its low gallons-per-flush figure with a redesigned bowl, a wider or faster flush valve and a glazed trapway, rather than simply shrinking the tank on an old design. The first generation of low-flow toilets in the early 1990s skipped that engineering, flushed weakly and earned low-flow toilets a bad reputation that took a decade to repair. Modern HETs were built specifically to end that problem.

The payoff is measurable and lasting. Toilets are the single largest source of indoor water use in a typical home, so trimming every flush by even a third of a gallon compounds into thousands of gallons saved each year. According to EPA WaterSense figures, replacing older inefficient toilets with certified high efficiency models saves the average household a meaningful share of its indoor water, and those savings show up directly on the monthly bill. We do not install or test toilets ourselves. Instead we compare manufacturer specifications, independent MaP (Maximum Performance) flush-test grams, EPA WaterSense listings, trapway geometry and the patterns across thousands of verified owner reviews. If you want the broadest performance-first ranking across every flush type, start with our guide to the best flushing toilets, then come back here to understand the HET category itself.

What Is a High Efficiency Toilet (HET)?

To break the definition into its parts, an HET is defined first by water use. Any toilet rated at 1.28 gallons per flush (often written 1.28 GPF or 4.8 liters per flush) or lower qualifies as high efficiency. That includes ultra high efficiency models that go down to 0.8 gallon and dual-flush models whose light flush sits near 0.8 to 1.0 gallon. The second part of the definition, the part that separates a real HET from a token one, is performance. A high efficiency toilet has to clear waste in a single flush, because an efficient toilet that needs a second pull is not efficient at all.

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TOTO Drake II

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TOTO Aquia IV

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American Standard Cadet 3

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The cleanest way to confirm both parts is the EPA WaterSense label. WaterSense certifies a toilet only if it uses 1.28 gallons or less and passes an independent flush-performance test, so every WaterSense toilet is an HET, and the label is publicly verifiable in a database at epa.gov/watersense. Not every HET carries the label, since certification is voluntary, but the labeled models are the ones with proven performance behind the efficiency claim. Vague marketing words like "eco," "green" or even "high efficiency" printed on a box without the WaterSense badge have no required testing behind them, so treat the certified models as the safe core of the category.

What Does HET Mean and Where Does 1.28 GPF Come From?

The history explains the number. The federal Energy Policy Act of 1992 capped new toilets at 1.6 gallons per flush starting in 1994, which made every legal new toilet a low-flow toilet by 1980s standards. When the EPA launched WaterSense in 2006 and applied it to toilets from 2007, it wanted a label that meant meaningfully better than the legal minimum, so it set the bar at a 20 percent reduction, which lands precisely at 1.28 gallons. Manufacturers adopted "high efficiency toilet" and the HET initialism to market models built to that 1.28-gallon level, and the terms stuck. Today the categories overlap almost perfectly: nearly every toilet sold as an HET is rated at 1.28 GPF, and nearly every WaterSense toilet is an HET.

It helps to keep three tiers straight. A standard toilet uses the legal maximum of 1.6 gallons. A high efficiency toilet uses 1.28 gallons or less, the WaterSense level. An ultra high efficiency toilet uses around 0.8 to 1.0 gallon, a smaller niche of certified models that save the most per flush but require an especially strong bowl design to keep clearing waste. For a side-by-side look at the two most common tiers, our explainer on 1.28 GPF vs 1.6 GPF toilets and which to choose walks through the annual water math.

How Much Water Does a High Efficiency Toilet Save?

The exact savings depend on what the HET replaces and how many people use it. Because toilets are the largest single source of indoor water use in most homes, even a small per-flush reduction compounds quickly across a year. Here is how the math works across the common standards.

To put numbers to it, a household that flushes about five times per person each day will, by switching from 1.6 to 1.28 gallons, save roughly 0.32 gallons on every one of those flushes. Across a year that adds up to thousands of gallons for a family of four, and the savings are dramatically larger when the toilet being replaced is a pre-1994 model using 3.5 gallons or more, where the per-flush difference is well over two gallons. Dual-flush HETs extend the savings further because most real-world flushes are liquid only, and the light flush on those models uses roughly 0.8 to 1.0 gallon, dragging average daily use below any single-flush model. For the wider efficiency picture, see our roundup of the best water saving toilets of 2026.

Do High Efficiency Toilets Flush as Well as Standard Toilets?

The key insight is that strong flushing and low water use stopped being opposites once manufacturers redesigned the bowl rather than just shrinking the tank. The leading HETs reach the same 1,000-gram MaP maximum as far thirstier older toilets, but they do it through better engineering instead of more water. TOTO's siphon designs, such as the Double Cyclone and Dynamax Tornado, prize a quiet, clean rinse that scours the whole bowl. Kohler's canister flushes, like Class Five and AquaPiston, release the full tank fast for a more forceful pull. A wide 3-inch flush valve, as on the American Standard Cadet 3, dumps the tank quickly for a faster, stronger flush than the 2-inch valves on cheap toilets. Pressure-assisted HETs from Gerber, such as the Avalanche, use compressed air to push water harder than gravity alone. Each is a different route to the same result: a 1.28-gallon flush that clears the bowl like a 1.6-gallon one used to. For the strongest flushers across every category, see our ranking of the best flushing toilets.

What Is a Good MaP Score for a High Efficiency Toilet?

MaP (Maximum Performance) is an independent test that publishes results at map-testing.com, and it measures how many grams of solid waste a toilet clears in a single flush against a 350-gram residential pass threshold. That threshold represents a realistic worst-case household load, so any score above it means the toilet should clear normal use in one flush. MaP matters even more for a high efficiency toilet than for a thirsty one, because the entire point of an HET is saving water, and a weak flush that needs a second pull wastes more than a strong single flush would have used, which defeats the purpose.

As a rule of thumb, treat 600 grams as fine for a light-use or guest bathroom, 800 grams as a strong everyday number, and 1,000 grams as the ceiling worth seeking if you have a large household, a history of clogs or simply never want to think about the handle twice. If a high efficiency toilet does not publish a MaP score at all, treat that silence as a warning sign rather than assuming the flush is strong. The leading HETs, like the TOTO Drake II, Kohler Cimarron and American Standard Cadet 3, publish a full 1,000-gram score at 1.28 gallons, which is the cleanest proof that efficiency and power coexist. For the very strongest single-flush performers, see our list of best EPA WaterSense certified toilets.

Are High Efficiency Toilets Worth It?

The old worry, that a low-flow toilet flushes weakly and needs a second pull, is exactly what the WaterSense performance test behind most HETs was created to rule out. A certified high efficiency toilet has to clear waste effectively to earn the label, so the modern models save water without the double-flushing that would erase those savings. Between a lower monthly bill, possible upfront rebates and identical flush power on the top models, there is little reason to choose a thirstier toilet for a typical home. The case is even stronger if you are replacing a pre-1994 toilet, where the water and cost savings are far larger. For models built around the lowest legal water level, see the best low flow toilets (1.28 GPF and under).

Are High Efficiency Toilets Required by Law?

It helps to separate two different rules. The federal Energy Policy Act has capped new toilets at 1.6 gallons per flush since 1994, so every legal new toilet in the country is already a low-flow toilet by 1990s standards. The high efficiency standard goes further, putting toilets at 1.28 gallons with verified performance through WaterSense. On top of those, a growing number of states have written the 1.28-gallon level into their own plumbing or efficiency codes, so in those states a new toilet effectively has to be high efficiency whether or not it carries the WaterSense badge. If you live in a water-stressed state, check your local code before buying, because a 1.6-gallon model may not be legal to install in new construction or a major remodel. Even where the law allows 1.6 gallons, the 1.28-gallon HET is almost always the smarter long-term choice.

Confirm the 1.28 GPF rating and verify the WaterSense model in the EPA database

The gallons-per-flush figure is what defines a high efficiency toilet, so confirm the listing reads 1.28 GPF or lower, and look for the blue WaterSense logo on the listing, the box or the specification sheet. Because the label can be misrepresented in third-party listings, the surest check is to search the model number in the public product database at epa.gov/watersense. If the exact model appears there, the certification and the efficiency claim are genuine. Avoid relying on vague words like "eco," "green" or even "high efficiency" printed without a verifiable certification behind them.

Pair the low GPF with a high MaP score so you never flush twice

A high efficiency toilet only saves water if it clears the bowl the first time. MaP measures how many grams of solid waste a toilet clears in one flush against a 350-gram residential pass threshold, and the HETs that reach 1,000 grams at 1.28 gallons, like the TOTO Drake II and American Standard Cadet 3, give you the rare combination of the lowest legal water use and a flush that never makes you reach for the handle again. Treat 800 grams as the floor for everyday use and 1,000 grams as ideal, especially for a large household or a history of clogs. A high efficiency toilet that hides its MaP score is one to skip.

Decide between single-flush simplicity and dual-flush savings

Single-flush HETs give one strong 1.28-gallon flush every time, which is the simplest path to both savings and reliability. Dual-flush models like the TOTO Aquia IV add a light flush of roughly 0.8 to 1.0 gallon for liquid waste, so their average daily water use drops below any single-flush model in a normal home. The trade-off is that everyone in the house has to pick the right button, and dual-flush models often post a slightly lower full-flush MaP. If maximum savings is the goal, choose dual-flush; if you want the simplest strong flush, a 1,000-gram single flush like the Drake II is hard to beat.

Favor a canister flush valve to hold the savings long term

A high efficiency toilet can quietly lose its savings if the flush valve leaks. A worn rubber flapper can let water seep from the tank into the bowl unnoticed, wasting gallons a day and silently undoing the whole point of an HET. Canister flush valves, such as Kohler's Class Five and AquaPiston designs on the Cimarron and Highline, seal across a wider surface and tend to hold tight far longer than a standard flapper, so the toilet keeps using only the 1.28 gallons it is rated for. If long-term efficiency matters to you, favor a canister-valve design, and after installation set the tank water level to the marked line and check periodically for a running tank.

Match the rough-in, bowl height and body style

Even the best high efficiency toilet is useless if it does not fit. Rough-in is the distance from the finished wall to the center of the floor-drain bolts, and most homes use 12 inches, though older houses sometimes have 10 or 14 inches. Comfort-height bowls sit around 16 to 17 inches off the floor and suit most adults and seniors, while standard height saves a little space. Decide between a one-piece like the TOTO UltraMax II, which has no tank-to-bowl seam to clean, and a two-piece like the Drake II, which is lighter and cheaper to ship. Value HETs from Woodbridge, such as the T-0001 and T-0019, and Swiss Madison's St. Tropez often bundle these features at a lower price, while Gerber's Viper and Avalanche are trusted in the trades. Confirm fit before buying so your HET installs cleanly the first time.