A dual flush toilet gives you two flushing options: a lower-volume flush for liquid waste and a full-volume flush for solid waste. Most models use less than a gallon of water for the partial flush and around 1.6 gallons for the full flush, letting you cut water use significantly on the majority of bathroom trips. The concept is simple, but the details around water savings, design types, and trade-offs are worth understanding if you’re considering one.
How a Dual Flush Toilet Works
Instead of one flush lever that releases the same amount of water every time, a dual flush toilet has two settings controlled by either a pair of buttons on top of the tank or a lever that moves in two directions. One option triggers a reduced flush (roughly 0.8 gallons or 3 liters) designed to clear liquid waste. The other triggers a full flush (about 1.6 gallons or 6 liters) for solid waste.
The most common design uses two buttons mounted on the tank lid, one larger and one smaller. The small button activates the partial flush, and the large button activates the full flush. Some wall-mounted models integrate the buttons into a flush plate on the wall above the toilet, which keeps the look minimal. Lever-style dual flush toilets exist too, where pushing the handle up triggers one volume and pushing it down triggers the other.
Where the Idea Came From
Bruce Thompson, who led the design team at Caroma Industries in Adelaide, Australia, developed the first dual flush cistern in 1980. Australia’s chronic water scarcity made conservation a practical necessity, and the Australian government backed the project with $130,000 in funding. When the system was trialed in a small South Australian town, it saved an estimated 32,000 liters of water per household per year. The design spread across Australia quickly and eventually became standard in much of the world, though adoption in the United States came much later.
How Much Water You Actually Save
The EPA estimates that switching to a dual flush toilet can save a household up to 4,000 gallons of water per year. That math makes sense when you consider that liquid waste accounts for the majority of flushes in a typical household. If most of your flushes use less than a gallon instead of 1.6 gallons (or more, if you’re replacing an older toilet), the daily savings add up fast.
To earn a WaterSense label from the EPA, a toilet’s rated flush volume cannot exceed 1.28 gallons per flush. For dual flush models, both the full flush and the reduced flush volumes must be specified, and the toilet has to meet the efficiency standard overall. That means even the full flush on a certified dual flush toilet uses less water than older standard toilets, which were designed around 3.5 gallons per flush before federal regulations lowered the limit in the 1990s.
Performance and Flushing Power
A common concern with low-water toilets is whether they can actually clear the bowl reliably. The industry uses a testing protocol called MaP (Maximum Performance) to measure this. During MaP testing, toilets are loaded with increasing amounts of test material until they fail to clear the bowl. The result is a score measured in grams. Toilets that score at least 600 grams earn a “MaP Premium” rating, which means they handle real-world waste volumes with no problems at a low water volume.
Many dual flush models score well in MaP testing, but not all of them are equal. If flushing power matters to you, checking a model’s MaP score before buying is one of the most reliable ways to compare options. Scores are publicly available through the MaP testing database.
Costs and Trade-Offs
Dual flush toilets typically cost more upfront than standard single flush models. The price gap varies, but you can expect to pay anywhere from $50 to $200 more depending on brand and features. Water bill savings help offset that difference over time, though how quickly depends on your household size, local water rates, and what toilet you’re replacing. A family of four replacing a 3.5-gallon vintage toilet will recoup costs far faster than a couple replacing a modern 1.6-gallon model.
The reduced flush does come with a practical downside: less water moving through the bowl means the bowl may not rinse as thoroughly, especially on the partial flush setting. Some owners find they need to clean the bowl more frequently than they did with a higher-volume toilet. This is a minor inconvenience for most people, but it’s worth knowing about upfront.
Retrofitting an Existing Toilet
If you don’t want to replace your entire toilet, dual flush conversion kits can add two-flush functionality to a standard single flush toilet. These kits replace the flush valve inside the tank and add a new button or lever mechanism. Most are designed for standard tank-type toilets, but compatibility varies by model, so checking the product specs against your toilet’s dimensions and flush valve size is important before purchasing. A conversion kit is a lower-cost way to try dual flush, typically running between $20 and $50, though the water savings may be slightly less precise than a purpose-built dual flush toilet.
Dual Flush vs. Standard Low-Flow Toilets
Modern single flush toilets already use 1.6 gallons per flush or less, which raises the question of whether dual flush is still worth it. The advantage comes down to averages. A single flush toilet uses the same volume every time regardless of what’s in the bowl. A dual flush toilet lets you use roughly half that volume on most flushes. Over thousands of flushes per year, that flexibility adds up to measurably lower water consumption, which is why dual flush remains the more efficient option in total household use even when compared to modern low-flow single flush models.