Dual Flush vs Single Flush: Water Use and Savings

How dual flush reduces water per flush

A dual-flush toilet gives you two flush options, normally selected by a separate button or lever position. The full-flush mode is designed for solid waste, while the reduced-flush mode uses a smaller volume of water to clear liquid waste. The EPA specifically points out that with a WaterSense labeled dual-flush toilet, you can save even more water by choosing the reduced-flush mode for liquid waste.

The practical result is that you no longer need the full 1.6-gallon federal-standard flush for every use. In a typical household, liquid waste is the more frequent flush, so the reduced-flush mode is available for the majority of flushes. This is why dual-flush toilets can outperform single-flush models on total water use even when both meet the same federal standard. Dual-flush mechanisms are explained in more detail here.

• Reduced-flush mode: uses a smaller water volume, intended for liquid waste
• Full-flush mode: uses the larger volume, intended for solid waste
• WaterSense labeled dual-flush toilets meet the same performance criteria as single-flush models
• The efficiency gain depends on actually using the reduced-flush option

Per-flush water volume: the numbers to know

The EPA gives three reference points for toilet water use. Older inefficient toilets can use as much as 6 gallons per flush, and the EPA calls them a major source of wasted water. The current federal standard is 1.6 gallons per flush. WaterSense labeled toilets use 1.28 gallons per flush or less, which is 20 percent less than the federal standard.

For a dual-flush toilet, the full-flush mode typically matches the volume of an equivalent single-flush model, while the reduced-flush mode drops to a smaller volume, designed specifically for liquid waste. The EPA notes that design improvements have allowed toilets to use 1.28 gallons per flush or less while still providing equal or superior performance.

If you are comparing models, the GPF rating tells you the full-flush volume. For reduced-flush volume, check the manufacturer's spec sheet, since it is not part of the standard labeling. The WaterSense certification is a reliable way to verify that a dual-flush toilet meets both efficiency and performance requirements.

What a household can actually save per year

The EPA estimates that replacing old, inefficient toilets with WaterSense labeled models can reduce a family's toilet water use by 20 to 60 percent. For the average home, that works out to nearly 13,000 gallons saved every year. Toilets are by far the main source of water use in the home, accounting for nearly 30 percent of indoor water consumption, so these savings are meaningful.

Nationally, if all old inefficient toilets in the United States were replaced with WaterSense labeled models, the EPA projects savings of more than 260 billion gallons of water per year. That is roughly the amount of water that flows over Niagara Falls in about five days.

Where does the 20 to 60 percent range come from? The low end represents efficient single-flush models. The higher end is achievable with dual-flush toilets when the reduced-flush mode is used regularly for liquid waste, since the per-flush volume drops below what any single-flush toilet can offer. For more on how toilet choice affects total household water, see our guide on toilet water usage by household.

Does performance suffer with dual flush?

This is the most common concern, and the answer is no, provided the toilet is WaterSense labeled. The EPA's WaterSense program independently certifies that toilets meet rigorous performance criteria, including the ability to clear waste from the bowl, clean the bowl surface, and transport waste through the drainline. These criteria apply equally to single-flush and dual-flush models.

Historically, the low-flow toilets of the 1990s had performance issues, which is why the EPA began certifying efficiency and performance together. Today, WaterSense labeled toilets, including dual-flush models, are designed to outperform older toilets from the 1980s and 1990s despite using significantly less water.

The reduced-flush mode is specifically engineered for liquid waste, which is why it does not need the same water volume as a full flush. As long as you use the reduced-flush mode for liquid waste and the full-flush mode for solid waste, performance should match what you expect from a single-flush toilet.

Which type is right for your bathroom?

If your goal is to minimize water use, a dual-flush WaterSense labeled toilet is the stronger choice, especially in a home with multiple people and frequent flushing. The reduced-flush mode gives you an additional saving that a single-flush toilet cannot match. If you want the simplest possible operation with no button choice to make, a single-flush WaterSense toilet still saves a significant amount of water compared with older models.

Consider your household. Elderly family members or young children may find two buttons confusing at first, though most people adjust quickly. For a guest bathroom, a single-flush toilet may be more foolproof, while a dual-flush toilet makes sense for the main bathroom where the choice becomes routine.

The flush volume also matters. If your home has older plumbing, a 1.28 GPF toilet may be a better match. If you are replacing a very old toilet, the savings from any WaterSense model will be substantial. You can compare the top options in our best dual-flush toilets and best single-flush toilets guides.

Common misconceptions about dual flush

A frequent misunderstanding is that dual-flush toilets use the same amount of water as single-flush models because the full-flush volume is similar. The saving comes from the reduced-flush mode, which is used for the majority of flushes in a typical home. If you never use the reduced-flush button, you will not see the full benefit.

Another misconception is that a smaller flush means a less powerful flush. The EPA's WaterSense performance criteria are designed to ensure equivalent performance, including in dual-flush models. The reduced-flush mode is not a weak flush, it is a targeted flush for liquid waste.

Finally, some people worry that dual-flush mechanisms are more prone to failure. The dual-flush valve is a mature design used by many manufacturers, and the same considerations that apply to any toilet, including flapper quality and maintenance, apply here. You can read more about flush control types to understand the options.

What to pick for your use

Questions

Is a dual-flush toilet really more water-efficient than a single-flush toilet?

Yes, when used correctly. The EPA notes that a WaterSense labeled dual-flush toilet can save even more water than a single-flush model by using the reduced-flush mode for liquid waste. The saving depends on using the smaller flush for liquid waste most of the time.

How much water does the reduced-flush mode use?

The EPA does not specify a single number for reduced-flush volume; it varies by model. The EPA confirms that reduced-flush mode uses a smaller volume of water than the full flush. Check the manufacturer's spec sheet for the exact reduced-flush volume of a particular model.

Are dual-flush toilets as effective at clearing waste?

WaterSense labeled dual-flush toilets must meet the same performance criteria as single-flush models, including waste extraction and bowl surface cleaning. The reduced-flush mode is engineered for liquid waste, so it does not need the same volume as a full flush.

Will a dual-flush toilet save water in a small household?

Yes, any household that regularly uses the reduced-flush mode for liquid waste will save water compared with using a full flush every time. The EPA estimates a 20 to 60 percent reduction in toilet water use when replacing old toilets with WaterSense models, with the higher end achievable through dual-flush use.

What if someone in the household always presses the full-flush button?

The toilet will still flush properly, and you will still be using a WaterSense compliant full-flush volume, which is more efficient than an old toilet. However, you will not capture the additional saving that the reduced-flush mode offers. This is mainly a consideration for guest bathrooms.