How to Adjust Toilet Flush Volume for Less Water

How toilet flush volume is determined

The amount of water your toilet uses per flush is set by two main parts: the fill valve and the flush valve. The fill valve controls how much water enters the tank after each flush, and the flush valve releases that water into the bowl. In most gravity-flush toilets, the water volume is directly tied to the tank water level, which is set by the float or ballcock in the fill valve.

The federal standard for new toilets is 1.6 gallons per flush, but many modern models use 1.28 gallons or less, and some dual-flush toilets use as little as 0.8 gallons for liquid waste. According to the EPA, toilets account for nearly 30 percent of indoor water use, so even small adjustments can make a noticeable difference in your water bill. For a deeper dive, see our toilet flush volume guide.

• Fill valve: controls when the tank stops filling, setting the water level
• Flush valve: releases the tank water into the bowl; its size affects flush power
• Dual-flush mechanism: offers a separate reduced flush for liquid waste

Adjusting the fill valve to lower tank water

The simplest way to reduce flush volume is to lower the water level in the tank. Most fill valves have an adjustment screw or a float arm that you can move to change the shut-off point. Turn the screw clockwise to lower the float, which stops the tank from filling as high. Check the manufacturer’s instructions for your specific fill valve model, as the adjustment method varies.

A good target is to set the water level so that the top of the water sits about one inch below the top of the overflow tube. If you set it too low, you may not have enough water to create a proper siphon, leading to weak flushes and clogs. Start with a small adjustment, flush, and assess the waste removal. If you find yourself double-flushing, you have turned it down too far. For more on tank water levels, see our guide to toilet tank water level.

Adjusting dual-flush settings

Many dual-flush toilets use a single fill valve but have a separate mechanism that controls how much water is released on the reduced flush. Some models allow you to adjust the reduced flush volume by changing the length of the flush valve lift, or by moving a dial on the flush valve's side. Consult your toilet's manual to see if your dual-flush system is adjustable. If you are unsure how your dual-flush mechanism works, our guide to how dual-flush toilets work can help.

If your dual-flush toilet is not adjustable, you can still reduce water use by ensuring the reduced flush button is actually being used for liquid waste. In many households, people habitually use the full flush, which defeats the purpose of the dual-flush design. If you are consistent about using the reduced flush, you can cut water usage significantly without any hardware changes.

Avoiding clogs: how low can you go?

The main risk of reducing flush volume is that you may not provide enough water to clear the bowl and the drain line. A toilet's flush performance depends on both the volume and the velocity of water. If you lower the tank water too much, the siphon might not form properly, leaving waste behind. The EPA's WaterSense program requires that labeled toilets pass rigorous performance tests, including waste extraction and bowl cleaning, at volumes of 1.28 gallons or less. This means modern toilets are designed to work well at low volumes, but older toilets may not be.

If you have an older toilet that uses more than 1.6 gallons, adjusting the fill valve may not give you a reliable result. In that case, it may be better to replace the toilet with a WaterSense labeled model, which is certified to use no more than 1.28 gallons per flush while still providing strong performance. You can compare WaterSense toilets or look for a dual-flush model if you want the option of an even lower reduced flush.

When to replace instead of adjust

Adjusting the fill valve is a free and quick fix, but it has limits. If your toilet is from the 1990s or earlier, it may use 3.5 to 6 gallons per flush, and simply lowering the water level might not yield enough savings. Also, if your toilet's flapper or flush valve is worn, you may be wasting water through leaks even after adjusting the fill valve. A leaky flapper is a common cause of a running toilet, and replacing it is a simple DIY project.

If you are considering a new toilet, look for one that is WaterSense labeled, which guarantees it uses 1.28 gallons per flush or less. Many utilities offer rebates for water-efficient toilets, and the savings on your water bill can offset the purchase price over time. For more information, see our guide to 1.28 GPF toilets or explore dual-flush options.

What to pick for your use

Questions

How much water can I save by adjusting the flush volume?

It depends on your current toilet and how much you lower the water level. If you have a 1.6 gpf toilet and adjust it down to 1.28 gpf, you save about 20 percent per flush. Over a year, that can add up to thousands of gallons for a typical family.

Will lowering the tank water level cause clogs?

If you set the water level too low, the flush may not have enough water to create a strong siphon, which can lead to incomplete waste removal and clogs. Make small adjustments and test the flush. If you need to double-flush, raise the water level back up.

Can I adjust the flush volume on a dual-flush toilet?

Many dual-flush toilets have an adjustable reduced flush volume, but not all. Check your owner's manual. If the reduced flush is not adjustable, you can still save water by consistently using the reduced button for liquid waste.

What is the easiest way to check if my toilet is wasting water?

Put a few drops of food coloring in the tank and wait 15 minutes without flushing. If the color appears in the bowl, you have a leak, often from a worn flapper. Replacing the flapper is a simple fix that can save up to 180 gallons per week, according to the EPA.