Do you still think that these two buttons are used just to empty the toilet?

Some systems use different opening levels or different activation mechanisms.

The user doesn’t need to understand the plumbing to operate it.

That’s one reason the buttons are placed directly on top of the tank.

They’re essentially giving you a simple interface for a more complicated mechanism underneath.

How Much Water Does Each Button Use?
There isn’t one universal amount.

The exact volume depends on the toilet model and its design.

EPA documents describe reduced-flush volumes in dual-flush tank toilets that can vary substantially between models. One EPA document describes reduced modes ranging from about 0.5 to 1.1 gallons per flush, while full flushes can reach up to 1.6 gallons in models covered by the earlier specification. (EPA NERL)

That’s why you shouldn’t assume that every “small button” uses exactly the same amount of water.

The best source for your particular toilet is its label, specification sheet, or manufacturer’s instructions.

Why Water Efficiency Matters
Toilets can account for a significant amount of water use in homes.

Every flush sends water through the toilet and into the wastewater system.

Multiply one flush by several people.

Then multiply that by every day of the year.

The numbers quickly become substantial.

That’s why water-efficient toilet designs have attracted so much attention.

EPA says replacing old, inefficient toilets with WaterSense-labeled models can reduce toilet water use by 20% to 60%, depending on what they replace and other factors. (US EPA)

The savings aren’t just theoretical.

Small differences repeated every day can add up.

But There’s a Catch
Here’s something many people don’t realize:

A dual-flush toilet only saves water if people actually use the reduced flush appropriately.

If everyone presses the full-flush button for every visit, the advantage of having two flushing modes can be reduced.

EPA has examined this issue and found that user behavior can affect the expected water savings from dual-flush designs. (US EPA)

In other words, the technology can provide the option.

But the person using the toilet still has to select the appropriate mode.

That’s why clear button designs matter.

The Buttons Can Be Surprisingly Confusing
You might think identifying the small flush would be obvious.

Apparently, it isn’t always.

EPA documentation discusses research into people’s ability to recognize the reduced-flush button. In one study involving 2,000 people and 18 dual-flush button designs, none of the designs achieved 100% recognition. (US EPA)

That’s fascinating.

It means that even when a toilet gives users a choice, the design of that choice matters.

If the buttons are confusing, people may press the wrong one.

And if users don’t understand the symbols, they may simply press whichever button looks easiest.

A tiny design decision can therefore influence water consumption.

What If You Press Both Buttons?
This depends on the specific toilet.