5 Tips for Choosing a Low-Flow Toilet

September 4, 2009 By Willem Maas

Whether your motivation is environmental responsibility, saving money, or meeting building codes, installing a more efficient toilet is an effective and easy way to upgrade your home.

Toilets consume an average of 20.1 gallons of water per person, per day in a home with no water-conserving fixtures, according to the American Water Works Association. That’s nearly 30 percent of an average home’s daily per-person indoor water use. Upgrading from a 3.5 gpf (gallons per flush) toilet to a 1.6 gpf model will reduce one person’s annual water use from 27,300 gallons to 12,500 gallons, according to the Federal Energy Management Program. Low-flow toilets save money, too: Replacing the showerheads and toilets in their home is saving Atlanta homeowners Judith and Tim Vanderver $148 per month on their water bill.

When low-flow toilets were introduced in 1994, stories of double flushing and clogging were widespread. But 1.6 gpf low-flow toilets have improved dramatically, and homeowner satisfaction has improved with them.

To increase the odds that your low-flow toilet experience will be positive, here’s what you should know before you buy:


While the technologies vary, what really matters is performance.

While the “behind the seat” technologies (dual flush, single flush, gravity fed, and pressure assist) vary, what really matters is performance.

The key measure of a toilet’s performance is how well it removes waste with a single flush. To assess performance, toilets have been tested since 1978 on their ability to flush up to 100 3/4-inch plastic balls. Other tests have been devised—by the manufacturers themselves, magazines like Consumer Reports, and third parties like the National Association of Home Builders (NAHB) Research Center—often with conflicting results.

One new testing protocol, called Maximum Performance (MaP) testing, has gained the support of 22 U.S. and Canadian water utilities as well as toilet manufacturers and government agencies. To better simulate real-world conditions, MaP testing uses soybean paste. The latest test results are published on the California Urban Water Conservation Council (CUWCC) website.


You’ll need a tool beside your toilet: do you prefer a plunger or a brush?

Toilets use either a siphonic or a wash-down method to remove waste from the bowl. The siphonic method, more common in North America, creates a siphon action that “pulls” waste from the bowl. The wash-down method, common in Europe, “pushes” waste out of the bowl. Because Europe has become a key market for dual-flush toilets, most dual-flush models use the wash-down method.

With the wash-down method, a much larger (up to four inches) trapway reduces clogging, but the smaller surface area of water in the bowl causes more of the dreaded “skid marks.” Siphonic designs provide a larger water spot, so there are fewer skid marks to clean. But the smaller trapway needed to create the siphonic action can result in more clogging.


Look for models that meet the new High Efficiency Toilet (HET) standard to maximize water and money savings.

The new HET standard defines a HET fixture as one that flushes at 20 percent below the 1.6 gpf maximum (that is, it has a maximum of 1.3 gpf). The CUWCC has published a list of HET incentive programs (PDF - Download) in California, Washington, Colorado, and Massachusetts.


In general, more expensive does not mean better.

When shopping for a new toilet, remember that there is little correlation between price and performance: Paying more for a toilet will not guarantee better flush performance! You can find single-flush toilets with excellent performance for less than $100, says John Koeller, technical advisor to the CUWCC. Prices for dual-flush toilets start at about $175. However, Koeller says, “good old competition among the manufacturers is driving dual-flush toilets down in price, bringing them closer to their single-flush cousins.”


To ensure comfort, try out a variety of toilets with different heights, seat shapes and rim designs.

Toilets come in a variety of designs. Introduced to meet requirements of the Americans with Disabilities Act, 17- to 19-inch toilets have become popular and are marketed as “comfort height.”

Bowls are available in elongated and round designs. While each has its proponents on the basis of comfort, there are space considerations. Before leaving on your toilet shopping trip, measure your bathroom to make sure there’s enough space for a toilet with an elongated bowl.

Koeller advises measuring not only the dimensions of your bathroom but also the distance from the floor flange bolt holes to the rear wall (known as the rough-in dimension). “Older homes, which tend to have smaller bathrooms, also tend to be sized for a 10-inch rough-in (rather than the 12-inch that is common in newer homes),” he says.

Tagged In: green tips, water saving, low flow toilet, dual flush toilet

Willem Maas

Willem Maas

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