Single vs Dual Flush: Which Saves More Water?

Flush volumes compared

A single flush toilet uses the same volume of water for every flush. The current federal standard allows up to 1.6 gallons per flush, but most new single flush models are designed around 1.28 gallons per flush or less, which EPA notes is 20 percent less than the federal standard. For more on what the gallon-per-flush rating means, see what is GPF.

A dual flush toilet gives you two choices. One control triggers a full flush for solid waste, and the other triggers a reduced flush for liquid waste. The reduced flush uses a smaller volume of water, and that is the whole point of the design. If you want to understand the mechanics, read how dual flush toilets work.

The actual flush volumes vary by model. WaterSense labeled toilets use 1.28 gallons per flush or less in the full flush mode, and the reduced flush typically uses a fraction of that. The exact reduced volume depends on the manufacturer and the specific design, but it is always smaller than the full flush.

How much water toilets use at home

Toilets are by far the main source of water use in the home, accounting for nearly 30 percent of indoor water consumption, according to the EPA. The average American family uses more than 300 gallons of water per day at home, with roughly 70 percent used indoors. That puts toilet flushes high on the list of things that move your water bill.

The biggest waste comes from older toilets. EPA notes that inefficient toilets using as much as 6 gallons per flush are a major source of wasted water. If your home still has one of those, replacing it matters far more than whether you pick single or dual flush.

Understanding your own water use is the first step. You can look at your water bill and see the total consumption, then estimate how much goes to flushing based on the number of people and their habits. Many households flush five to seven times per day per person, but that number varies widely. The key takeaway is that the toilet is a major consumer, so efficiency here has an outsized impact.

Real savings from upgrading

EPA estimates that replacing old, inefficient toilets with WaterSense labeled models reduces the water used for toilets by 20 to 60 percent, or nearly 13,000 gallons per year for the average home. The exact amount depends on household size, flush frequency, and how old the old toilet is.

The savings come from the flush volume itself, not from the brand or the model. A WaterSense labeled toilet uses 1.28 gallons per flush or less, and that label is independently certified. Learn what the label means at WaterSense certification.

Note that dual flush toilets have a slightly different certification path. Under the current WaterSense specification (Version 1.2), dual flush models use an effective flush volume calculation that averages the full and reduced flushes. For the latest on specification changes, refer to the official EPA document.

Even if you already have a 1.6-gallon-per-flush toilet, switching to a 1.28-gallon model cuts water use by 20 percent per flush. That is the same reduction the EPA highlights. If you have an older 3.5 or 5-gallon toilet, the savings are proportionally larger.

When dual flush saves more water

The reduced flush mode is the only feature that separates a dual flush toilet from a single flush model. If you always press the full flush button, you get the same water use as a single flush toilet, and the dual flush advantage disappears. EPA specifically notes that a WaterSense labeled dual flush toilet saves even more water when you choose the reduced flush mode for liquid waste.

In a typical household, liquid flushes are the majority of flushes, so the savings accumulate quickly. A study from the EPA's WaterSense program suggests that a dual flush toilet can reduce total toilet water use by an additional 20 to 30 percent compared to an efficient single flush model, depending on user behavior. The tradeoff is simplicity. A single flush toilet has one lever and one outcome. A dual flush requires you to choose the right button. If you or anyone in your home will not bother, single flush is the safer choice.

There is also a hybrid option: choosing a single flush model that uses the lowest full flush volume, which gives you most of the savings without the second control. For a fuller comparison of the two designs, see single vs dual flush toilets.

Another consideration is whether the reduced flush is strong enough to clear the bowl. EPA's WaterSense performance criteria include waste extraction and bowl cleaning tests, and every labeled model must pass them. That means a reduced flush is not a weak flush; it is simply calibrated for liquid waste.

What to pick for your bathroom

The answer depends on your habits. If you want the lowest possible water use and you will actually use the reduced flush for liquid waste, pick a dual flush toilet. If you want one predictable flush and do not want to think about buttons, pick a single flush model at 1.28 gallons per flush or less.

Replace old 6-gallon-per-flush toilets first. That is where the biggest water savings live. The EPA's replacement guidance shows a 20 to 60 percent reduction in toilet water use, which is far larger than the difference between two new efficient models. Browse the best dual flush toilets, the best single flush toilets, or the best 1.28 gpf toilets to start.

If you have a two-piece toilet and prefer a classic look, a dual flush two-piece may suit you; if space is tight, consider a round bowl model. Always check the rough-in size to ensure a proper fit, as described in toilet rough-in sizes.

What to pick for your use

Questions

Does a dual flush toilet always save more water than a single flush toilet?

No. A dual flush toilet only saves water when you use the reduced flush for liquid waste. If you always use the full flush, it uses the same volume as a comparable single flush model.

What is the federal standard for toilet flush volume?

The current federal standard allows up to 1.6 gallons per flush. WaterSense labeled toilets use 1.28 gallons per flush or less, which is 20 percent less than the standard.

How much water can I save by replacing an old toilet?

EPA estimates that replacing old, inefficient toilets with WaterSense labeled models reduces water used for toilets by 20 to 60 percent, nearly 13,000 gallons per year for the average home.

Is the reduced flush enough to clear the bowl?

EPA's performance criteria for WaterSense labeled toilets include waste extraction and bowl cleaning tests. Every labeled model is independently certified to those requirements.

Which is better for a small bathroom?

Space depends more on the bowl shape and rough-in than on the flush type. Both single and dual flush toilets come in compact and round designs.

Are there any downsides to dual flush toilets?

The main downside is user error: if the wrong button is pressed, you may use more water than needed. Also, some dual flush models have more parts that could need maintenance, though modern designs are reliable.