When it comes to the systems in the home that help with lighting, food prep, bathing, and more, it's important to have at least a basic understanding of how they work. Without this knowledge, it can be difficult to choose appropriate replacement fixtures or upgrades that suit the needs of the home while remaining within the limits of the current infrastructure. This includes learning what gallons per flush (GPF) means and how this metric affects the function of your toilet.
By gaining a better understanding of the GPF of the toilet, it becomes easier to see the effects of excessive flushing or unreasonable water usage on your bills. This metric is even used by the government to limit the water usage of standard toilets and improve water conservation across the country. So, what are gallons per flush?
Gallons Per Flush (GPM)
Strictly speaking, gallons per flush or GPF is a metric to measure the volume of water a toilet uses with each flush. This measurement varies between toilet brands and specific toilet models. In the past, toilets that used more than 3 gallons per flush were normal throughout homes in America, but some toilets used up to 7 gallons per flush, which roughly equals about 42 gallons per day. In order to increase water conservation efforts, a national standard of 1.6 GPF was instituted in 1992, taking full effect in 1994.
Given that the EPA lists the toilet as the largest source of water use in the home, any reduction in the GPF of a toilet without detracting from the functionality of the fixture reduces water bills and improves water conservation. However, if the GPF of a toilet is too low, then it may have problems flushing heavy waste, resulting in recurring clogs and messy toilet bowls that need to be cleaned frequently. Keep GPF in mind when you are looking for a toilet replacement or upgrade so that you can confidently choose a toilet with appropriate flushing power for your family while reducing the water consumption of the home and saving on the water bill.
National Water Efficiency Standards
For the purpose of improving environmental protection and conservation efforts across the country, Congress and President George H.W. Bush signed the Energy Policy Act (EPAct) in 1992 that included national water efficiency standards for toilets, faucets, and showerheads. This means that there are legal regulations in place to limit the amount of water a toilet can use to 1.6 gallons per flush. The EPAct took full effect in the industry two years later in 1994, but toilets that were manufactured prior to 1994 are still found in many homes.
These relics from almost three decades ago could use up to 7 gallons per flush or about 42 gallons of water per day, while a standard toilet made after 1994 is limited to just 1.6 GPF, or about 9.6 gallons per day. This significant decrease in daily water use isn't just great news for water conservation efforts: It will also lower your water bill and keep more money in your pocket, so if you have an older toilet with a high GPF, it may be time to make the change to a more efficient toilet.
To help consumers find appropriate toilet replacements or upgrades, the EPA create the WaterSense certification, which is similar to the EnergyStar program for appliances. Toilets that use at least 20 percent less water than the 1.6 GPF standard can receive the WaterSense certification. These models typically have a GPF rate of about 1.2.
Find Your Toilet’s GPF
It's never a bad idea to have all the information on your current plumbing infrastructure, especially given that a toilet uses about 30 percent of the water that comes into the home. If you don't know the GPF of your toilet, then you may be spending significantly more on your water bill than necessary. However, manufacturers understand the importance of this measurement and typically list the GPF in an easy-to-see location on the body of the toilet.
The most common spot to find this information is between the seat and the tank. There is typically a stamp on the porcelain that lists the gallons per flush measurement. If this spot on the toilet is blank, then the GPF may be stamped on the underside of the tank lid or even inside the tank on one of the walls. Keep in mind that if your toilet was manufactured after 1994, then it's likely that the gallons per flush measurement for your toilet is 1.6 GPF or lower. Dual flush toilets may list two GPF measurements: A lower flush volume for flushing liquids and a higher flush volume for solids.
If your toilet doesn't list the GPF, you can still figure it out by taking a few quick measurements and making some simple calculations.
It's a little bit more difficult to figure out the GPF if it isn't listed clearly on the body of the toilet, but as long as you have a tape measure, a calculator, and a basic understanding of mathematics, you can calculate the GPF with minimal effort.
Extend the end of the measuring tape down into the toilet tank and write down the water level in inches. Keep the tape measure in place and flush the toilet to drain the water. Some water will likely stay in the bottom of the tank during the flush. Record the lowest water level in inches and subtract this second reading from the first to get the height.
Measure across the length and width of the tank, recording both numbers, then multiply the height by the length by the width to find the volume of water in cubic inches. Divide this total by 231 to convert your findings from cubic inches to gallons.
First water level reading: 5.5
Second water level reading: 0.6
Height = 5.5 – 0.6 = 4.9
Length = 15.0
Width = 5.0
Volume (cubic inches) = 4.9 x 15.0 x 5.0 = 367.5
Convert to gallons = 367.5 / 231 = 1.6 gallons
While modern toilets are limited to just 1.6 GPF, you can get models with a pressure-assist unit that can flush a 1.6-gallon tank with the force of a 5.5-gallon flush. Just keep in mind that these units are noisy and only work in toilets that are designed for pressure-assist units.
Water Efficiency Management Guide. Environmental Protection Agency.
Residential Toilets. Environmental Protection Agency.