Gallons per flush (GPF) is a measurement used to rate the water usage of toilets and urinals. It refers to the number of gallons of water used per flush. Understanding GPF is important for choosing water-efficient plumbing fixtures and appliances.
A Brief History of Gallons Per Flush
Older toilets, before 1992, used 3.5 gallons or more per flush. This was incredibly wasteful, especially considering that millions of flushes happen every day.
In 1992, the US Energy Policy Act was passed, which mandated that all new toilets sold in the US must use 1.6 GPF or less. This greatly reduced water consumption. Modern high-efficiency toilets use only 1.28 GPF. Some ultra-low flow toilets use 0.8 GPF or even less.
Here is a quick history of toilet GPF:
- Before 1950s – 5+ GPF
- 1950s – 3.5 GPF
- 1992 – 1.6 GPF mandated
- Now – 1.28 GPF or less for high-efficiency models
As you can see, the GPF used by toilets has dramatically reduced over time. This has saved significant amounts of water nationwide.
Why Gallons Per Flush Matters
The GPF directly impacts how much water a toilet uses. A lower GPF means less water is required per flush. Here are some key reasons why GPF matters:
- Water conservation – Lower GPF saves large amounts of water, especially for households and businesses with high toilet usage. This preserves water supplies.
- Saves money – Using less water per flush reduces utility bills. Low-flow toilets use 30-60% less water than standard 1.6 GPF models.
- Environmental impact – It takes energy to supply, deliver, and treat water. Reduced GPF lowers the environmental footprint.
- Performance – Modern low-flow toilets are engineered to flush efficiently and prevent clogs despite using less water.
- Building codes – Plumbing codes require new construction and renovations to install 1.6 GPF toilets or better. Low GPF is mandatory.
Choosing fixtures with low gallons per flush is an easy way to conserve water and realize cost savings over time.
How Gallons Per Flush is Measured
The GPF of toilets and urinals is tested and rated using standardized test procedures developed by the EPA WaterSense program. This ensures accurate ratings across different models.
There are two main methods:
Gravity Tank Toilets
For tank-style toilets, the tank is filled to a preset level. Then, the toilet is flushed and the water released from the tank is captured and measured. This directly measures the water used per flush.
Flushometer Valve Toilets
These are commercial pressure-assisted units often used in public restrooms. For these tests, the water supply line is fitted with a flow meter to measure the volume released during the flush cycle.
For urinals, the flush duration is measured and used to calculate the GPF based on the fixture’s flow rate.
Manufacturers test their products and report the certified GPF ratings. Consumers can easily compare ratings when shopping for plumbing fixtures.
Common Gallons Per Flush Ratings
Here are some of the most common GPF ratings for toilet fixtures:
- 1.6 GPF – The baseline standard for new toilets sold since 1994. Offers significant water savings over older 3.5+ GPF units.
- 1.28 GPF – The current standard for high-efficiency toilets. At least 20% less water than 1.6 GPF. Qualifies most models for WaterSense certification.
- 1.0 GPF or less – Ultra low-flow units that use 1 gallon or less per flush. Includes dual-flush models with 0.8/1.6 GPF settings. Maximum water conservation.
- 3.5+ GPF – Found in older toilets from the 1980s and earlier. Very inefficient by today’s standards. Should be replaced with 1.28 GPF or better models.
- 0.5 – 0.8 GPF – Extreme low-flow toilets. Provide the highest possible water savings but may require multiple flushes. Rarely used in residential settings.
As a general rule, choose the lowest gallons per flush within your budget constraints. 1.28 GPF high-efficiency toilets offer a good balance of water savings and reliable performance for most homes and businesses.
Factors That Determine Gallons per Flush
Several technical factors influence the water usage and rated GPF of a toilet fixture:
- Tank size – Larger tanks hold more water to start with, increasing GPF. Typical tank sizes are 1.6 or 3.5 gallons.
- Trapway size – Wider trapways require more water volume to flush effectively. Buttrapways have narrowed on low-flow models.
- Flushing mechanisms – Includes flapper valves, pressure-assisted flushers, vacuum systems, siphon jet designs, and dual flush mechanisms. More efficient designs reduce GPF.
- Water surface tension – Smoother glazes and bowl shapes improve surface tension so less water is needed.
- Water pressure – Higher water pressure enables complete flushing with less water. Some toilets have minimum pressure requirements.
- Leakage rates – Small leaks add up over time. Low leakage saves water between flushes.
Manufacturers optimize these factors to achieve complete, reliable flushing with the lowest possible water usage.
Gallons Per Flush Requirements by Code
Most areas regulate the maximum GPF allowed for new construction and remodels. Common requirements:
- International Plumbing Code – 1.6 GPF toilets
- EPA WaterSense – 1.28 GPF or less
- California Green Building Code – 1.28 GPF toilets
- LEED Building Standards – 1.28 GPF or dual-flush
Older 3.5+ GPF toilets exceed the allowed GPF in most areas when retrofitting or replacing existing fixtures. Be sure to check your local codes for the exact GPF limits.
Finding a Toilet’s Gallons Per Flush
You can determine the GPF of any toilet by:
- Checking the tank – There is often a GPF rating printed inside the tank or on the bowl behind the seat.
- Looking at the specifications – Product manuals and spec sheets list the official GPF.
- Scanning the packaging – Most toilets have a label or sticker indicating the GPF.
- Checking the bowl shape – Elongated bowls often indicate 1.6 GPF or higher. Round front bowls are typically 1.28 GPF or less.
- Knowing the age – Older units made before 1994 are very likely 3.5 GPF models or higher.
If no rating is visible, you can manually measure the GPF following the water supply methods described earlier. This will determine the exact flush volume.
Toilet Types by Gallons Per Flush
Here is an overview of some common toilet types organized by typical GPF ratings:
Low-Flow Toilets (1.6 GPF)
- One-piece elongated 1.6 GPF
- Two-piece round front 1.6 GPF
- Commercial pressure-assist 1.6 GPF
These offer moderate water savings versus older 3.5+ GPF models. 1.6 GPF was the federal standard from 1994 to 2014. Any toilet made in this period likely has a 1.6 GPF rating unless otherwise labeled.
High-Efficiency Toilets (1.28 GPF or Less)
- One-piece dual flush 1.28/0.8 GPF
- Two-piece elongated 1.28 GPF
- Macerating composting toilet 0.8-1.0 GPF
- Wall-mount WaterSense 1.28 GPF
These are the current standard for new construction and remodeling projects. WaterSense certification generally requires 1.28 GPF or lower.
Ultra Low-Flow Toilets (1.0 GPF or Less)
- Pressure-assisted 0.8 GPF
- Vacuum-assist 0.8 GPF
- Dual flush round front 0.8/1.6 GPF
- Composting toilet 0-0.5 GPF
Extreme water savers but may require trade-offs. Best for dedicated half-baths and powder rooms. More likely to need multiple flushes.
Outdated Toilets (3.5+ GPF)
- Older 3.5 GPF tank toilet
- Flushometer valve 3.5+ GPF
- Vintage washdown 5-7 GPF
These older toilets are water guzzlers by modern standards. Most plumbing codes require replacement with 1.28 GPF or dual flush models when remodeling.
Selecting a Toilet by Gallons Per Flush
Use this process when selecting a toilet based on desired water efficiency:
- Check local plumbing codes for minimum allowed GPF. This sets the baseline.
- Determine if you want standard 1.6 GPF or higher-efficiency 1.28 GPF models. 1.28 GPF offers greater water savings.
- Consider your needs – full baths may need 1.6 GPF to prevent clogs. Half-baths can use ultra low-flow 0.8 GPF.
- Compare ratings of models in your preferred style – one-piece, two-piece, wall-mount, etc.
- Validate WaterSense certification on models claiming 1.28 GPF or lower. This confirms reliable performance.
- Choose the toilet with the lowest GPF rating that fits your requirements and preferences.
Prioritizing gallons per flush when shopping ensures you select the most water-efficient toilet for your specific needs.
Gallons Per Flush for Urinals
Urinals are a major source of water use in commercial restrooms. Typical GPF:
- Older Urinals – 1.0+ GPF
- Modern Urinals – 0.5 – 0.125 GPF
- Waterless Urinals – 0 GPF
Many jurisdictions now require 0.5 GPF or lower on new urinal installations. Waterless zero-flush urinals are growing in popularity.
Proper urinal GPF selection reduces water waste while supporting heavy traffic. Low-flow models still provide effective flushing action with less water.
Dual-Flush Toilet Systems
Dual-flush toilets offer a choice of two flush settings:
- Full flush – 1.6 GPF for solid waste removal
- Reduced flush – 0.8-1.0 GPF for liquid waste only
Users simply push the proper button. The two-setting system provides maximum efficiency for each use case. Average dual flush toilet water usage is about 1.28 GPF when accounting for all flushes.
Dual-flush mechanisms are available on many high-efficiency and WaterSense certified toilet models. The added flexibility helps conserve water.
How Much Water Can Low-Flow Toilets Save?
Here are some savings estimates for replacing a 3.5 GPF toilet with a more efficient 1.28 GPF high-efficiency model:
- Household of 4 – Saves 18,000 gallons per year
- Office with 20 employees – Saves 30,000 gallons per year
- Restaurant with restrooms – Saves 456,000 gallons per year
The savings quickly add up for high-traffic restrooms. Low-flow models use 30%-60% less water overall.
Replacing all 3.5+ GPF toilets can save thousands to millions of gallons, depending on the context. It is one of the most effective ways to reduce water consumption.
Is GPF the Only Factor in Toilet Efficiency?
While GPF directly affects water usage, other factors also contribute to toilet efficiency:
- Waste removal – Bowl shape and flushing power must effectively clear waste.
- Leak prevention – Small leaks add up. Quality parts prevent leakage over time.
- Chemical resistance – Materials must withstand cleaning chemicals to prevent premature wear.
- Fixture longevity – Well-made products have long lifespans, saving the environmental costs of replacement.
The most efficient toilets combine effective flushing and low GPF with durability, leak prevention, and longevity.
Finding Toilets with Low Gallons Per Flush
Here are some recommendations for locating quality low-GPF toilets:
- Check for WaterSense certification – This label ensures a 1.28 GPF or lower rating plus reliable performance. WaterSense models are ideal for most homes and businesses.
- Select reputable brands – Top manufacturers like American Standard, Kohler, and Toto engineer high-performing low-flow toilets.
- Visit a plumbing showroom – Knowledgeable staff can explain the latest water-saving options and recommend models ideal for your needs.
- Look for the latest technology – New innovations like dual-flush, pressure-assist, vacuum, and siphon jet improve efficiency.
- Compare ratings online – Check GPF specs and read reviews of current models to choose quality low-flow toilets.
With so many choices available, it’s easy to save water and money by installing an efficient low-GPF toilet.
Low-Flow Toilet Troubleshooting
While low-flow toilets offer major water savings, some users report issues like multiple flushing or clogging. Here are some common remedies:
- Use a plunger – A forceful plunge can help clear minor clogs. Alternate repeated plunges and flushes.
- Adjust the flush valve – Make sure flapper chains have the proper slack and the tank water level is set correctly.
- Check for leaks – Small leaks that continuously refill the tank raise the average GPF. Fix any leaks.
- Upgrade components – Install an improved flapper, gaskets, and fill valve if existing parts fail prematurely.
- Clear the rim jets – Remove obstructions and limescale from the rim water jets.
- Avoid overuse of cleaning chemicals – Harsh chemicals can degrade toilet seals and gaskets over time.
With routine maintenance and occasional upgrades, most low-flow toilets can operate efficiently for years.
Gallons Per Flush Regulations and Building Standards
Various regulations and codes mandate low-flow fixtures to conserve water:
- EPA WaterSense – Voluntary program promoting 1.28 GPF toilets or lower. Must pass rigorous performance testing.
- LEED Building Standards – Awards points for 1.28 GPF/dual-flush toilets to obtain green building certification.
- International Green Construction Code (IgCC) – Requires 1.28 GPF toilets for new commercial buildings.
- CALGreen Code – California mandates 1.28 GPF toilets and 0.5 GPF urinals for all new construction.
These and local ordinances ensure new buildings minimize water waste. Check your regional codes for specific GPF requirements. Installing WaterSense fixtures simplifies compliance.
Gallons Per Flush and Water Efficient Landscaping
Low-GPF plumbing is just one aspect of sustainable water management. Other strategies include:
- Drought-tolerant native plants and grasses – Reduce irrigation needs.
- Smart irrigation controllers – Custom watering schedules match weather and soil moisture.
- Greywater reuse – Repurpose household wastewater for landscape irrigation.
- Rainwater harvesting – Capture and store rainwater from roofs.
- Low-flow showerheads and faucets – Limit indoor water use.
Combining low-GPF fixtures with other water-wise practices maximizes conservation benefits both indoors and outdoors.
Conclusion
Understanding and selecting plumbing fixtures based on their rated gallons per flush is an essential step in building and remodeling water-efficient homes and buildings. Federal mandates have reduced toilet GPF from over 5 GPF to 1.6 GPF or lower over recent decades.
Choosing WaterSense certified toilets and urinals with a 1.28 GPF rating or better provides maximum water savings and prevents waste while still delivering effective performance. Combined with other conservation tactics, low-GPF fixtures are key to establishing overall sustainability.
FAQ About Gallons Per Flush
Below are answers to some frequently asked questions about gallons per flush.
What is the minimum GPF for new toilets?
Since 1994, the minimum GPF allowed for new toilet sales in the US is 1.6 GPF. Most plumbing codes now require high-efficiency 1.28 GPF for new construction and remodeling.
How much water do newer low-flow toilets use?
Quality low-flow toilets have a rating of 1.28 GPF or less. Top WaterSense certified models use a maximum of 1.28 gallons per flush.
Do low-GPF toilets work effectively?
When engineered properly, low-flow 1.28 GPF and dual-flush toilets provide reliable flushing and waste removal comparable to less efficient 1.6+ GPF models.
Do low-flow toilets clog more easily?
Some earlier low-flow toilets had problems with clogging, but modern 1.28 GPF designs have greatly improved. Proper installation and maintenance also prevents clogs.
How many times must you flush a low-flow toilet?
Quality 1.28 GPF high-efficiency toilets and most dual-flush models only require one flush to fully clear waste from the bowl. Multiple flushing indicates an underlying problem.
Do low-flow toilets require more cleaning?
No, 1.28 GPF WaterSense toilets stay just as clean as higher-flow models. Some older 0.8 GPF units may require more frequent cleaning.
