Just how many gallons per flush
does a 7-year-old, 1.6-gpf toilet actually flush?
Hint: It's not necessarily 1.6 gallons.

Who doesn't get worse for wear the older he gets? A recent study by two Arizona researchers indicates low-flow toilets aren't any different.

Who doesn't get worse for wear the older he gets? A recent study by two Arizona researchers indicates low-flow toilets aren't any different.

On average all the low-flow toilets put in service seven years ago used almost 2 gallons to flush - about 25 percent more water than they should. Furthermore, more than a quarter of the households studied had at least one 1.6-gpf toilet that routinely used more than 2.2 gpf. Combine these high flush volumes with frequent incidences of double-flushing and flapper leaks, and you've got another big problem just now getting noticed.

As a result, the researchers recommend the water-savings projections calculated by local water officials at the beginning of the rebate program be adjusted downward over the expected 20-year life of the rebate toilets.

That's not all the recommendations either. We'll get to that part later (and we know you aren't going to like it.)

As researchers Jim Henderson and Gary Woodward point out in a study released late last year, what we know about low-flow toilets we know from research done just a year after the water closets were installed. Past this point in time, no studies had ever gathered data on the functioning of older low-flow toilets by measuring the water flow rate straight from the water meter. And no consumer satisfaction studies had ever been done on older toilets either.

The researchers considered their investigation doubly important since "even though low-consumption toilet performance has improved since the first models, many current models still rely on the same adjustments to the 3.5-gallon toilet."

In other words, if the common flapper and toilet dam modifications originally introduced in the first-generation 1.6-gpf toilets aren't working properly now, problems were only going to multiply from this point forward as more low-flow toilets are put in service.

Beyond documenting a decline in performance due to aging, the two were also concerned about the "alterability" of many brands, whether it be done intentionally or inadvertently.

"Lack of correct replacement parts seems a likely contributor to a possible decline in toilet performance with age, as early-close flappers are replaced with generic flappers, which allow a 3.5-gallon flush É" Also, while the researchers seem willing to give homeowners a pass on buying the wrong kind of flapper, they believe that toilet dams "can be easily disabled, although not so easily as to be removed unwittingly."

The Research

Like many other American cities, Tucson, Ariz., implemented a rebate program in 1991-92 to retrofit 3.5-gpf toilets. Henderson and Woodward selected households that participated in the rebate program for their study.

Data loggers were attached to the water meter on the water line entering each home, and four days worth of data at 10-second intervals were recorded. Data gathered from 170 homes were analyzed using specialized software for identifying toilet flushes. Toilet flushes were measured according to their peak flow, duration and volume of flush and compared to the expected inventory of toilets in the home.

Afterward, a follow-up survey confirmed the number and type of toilets in the household, asked about toilet function problems, and elicited a rating of owner satisfaction with the function of these low-flow toilets.

In all, the research contained information on the performance of 20 different low-flow models with various flush mechanisms installed during the rebate program.

The three main problems documented with the low-flows were high flush volume, double flushing, and flapper leaks:

High Flush Volume

The average flush volume for all rebate toilets was 1.98 gpf, or about 24 percent higher than what they were designed to use. But that only tells part of the story.

More specifically, only low-flows with average flush volumes greater than 2.2 gpf were classified as "high flush" volumes. (The 2.2-gpf figure is also the highest allowed flush volume allowed for any of the flushes used in meeting AMSE/ANSI low-flow testing protocol.)

More than a quarter of the homes surveyed had at least one low-flow toilet with an average flush volume greater than 2.2 gpf. (Log on to Pmmag.com for details on performance per flush mechanism, including pressurized models.)

While water pressure variations could possibly affect flush volume, the researchers concluded that was not case with their study.

"Average water pressure varies by 5 to 10 psi across pressure zones in the central city, and by 10 to 20 psi in the higher elevation portions of the service area," the report states. "Differences in pressure of 20 psi would be large enough to cause small systematic variations in flush volume in some toilets, but not enough to cause flush volumes of 1.6-gallon toilets to consistently be measured above 2.2 gpf."

Double Flushing

Chronic double flushing occurred in almost 11 percent of the rebated toilets. Only toilet flushes from the same device within four minutes of each other were counted as "multiple" flush events. The proportion of possible multiple flushes to total flushes for toilets in each home was recorded. Toilets with multiple flushes greater than or equal to 15 percent were classified as having a problem with double flushing.

"This is a conservative standard," the report says. "With an average of 28 flushes per toilet over a four-day period during the study, this means at least four multiple flushing events, or one per day, were needed for multiple flushing to be considered a problem."

Interestingly enough, data logging revealed that double flushing also occurred in the homes' 3.5-gpf toilets, that for one reason or another, had not been retrofitted. While the double flushing occurred less frequently with 3.5-gpf toilets - 6.6 percent vs. 10.9 percent - the condition is not just associated with 1.6-gpf toilets.

In follow-up phone interviews, homeowners were allowed to use their own standard to determine what they determined to be a problem with double flushing. Based on these answers, 38 percent of low-flow toilets required frequent double flushing. "This result indicates that many homeowners considered double flushing to be a problem even if it occurs less than once per day," the research states.

Flapper Leaks

While a toilet can be expected to last 20 years, a typical flapper will last about five years. In other words, three flappers can be expected to be installed over the life of one toilet.

A couple of factors need to be considered for flappers other than just everyday wear and tear. High concentration of choloramine, a residual disinfectant used in some water systems, deteriorates some flappers. Also, the Tidy Bowel Man might be a culprit, too. Testing done by the Metropolitan Water District of Southern California showed that "halogenating" bowl cleaner (i.e., typically, a cleaning product designed to sit in a toilet tank), could lead to rapid deterioration and warping of flappers. Keep in mind that the testing was done in 1994. Since then, manufacturers have improved their flappers. MWD tests done again in 1998 showed that some new flappers were "either not affected, or much less affected" by halogenating bowl cleaners.

As a result of these circumstances, at least 12 percent of the households had recurring flapper leaks in their low-flow toilets. Flapper leaks, however, were also identified in the old 3.5-gpf toilets, too. "Flapper leaks occurred at a higher rate in low-consumption rebate toilets than in nonlow-consumpution, nonrebate toilets," the researchers write, "but it was not possible to determine the exact amount of difference in the rate of flapper leaks because of the difficulties in determining the source of some flapper leaks."

The additional legwork done by the researchers, however, shows that God only knows what kind of flappers are being used in weekend DIY projects. (For more on this, see our sidebar, "Cure-All Or Curse-All.")

Based on their work, the researchers make several recommendations, including, word-for-word, the following:

  • The water industry should collectively press through the ASME standards process for toilet designs which are not alterable. This means casting toilet dams as part of the tank, if a toilet dam is used. This would also mean using tanks with low-consumption capacity that do not require an early-close flapper. Toilets with specialized flush mechanisms should be made so a 3.5-gallon per flush replacement mechanism will not fit into a toilet that was designed to flush 1.6 gallons.

  • The water industry should not offer rebates or direct install programs which include toilets with alterable designs or with specialized parts for which replacements may not be readily available later in the life of the toilet.
We told you you wouldn't like this part. While one research project doesn't make a bandwagon, many other cities around the country big and small orchestrated similar rebate programs. We have a feeling other researchers and ultimately regulators will be climbing on board the bandwagon soon.

Curse-All Or Cure-All?

We think the recommendations discussed in the main story are more cure-all than curse-all.

Can manufacturers cast a toilet dam as a permanent part of the tank? It wouldn't be easy. Toilets start out life as clay and clay contains a lot of moisture. As a result, a toilet is all that more larger before it hits the kiln. China isn't the best medium for creating a line of fixtures with over-exacting dimensions, particularly on anything inside the toilet.

For example, do you think a 2-inch trap measures exactly 2 inches? It doesn't. Not exactly anyway.

Due to such minor variations, plumbers have to able to fine-tune each toilet upon installation. Contractors can try baffles of various diameters, for example, to easily adjust early-close flappers. It's this kind of "alterability" that makes a low-flow toilet remain a low-flow toilet.

The researchers also seem to have it in for early-close flappers altogether. However, their own research shows this type of flush mechanism perform well. "Despite the ease with which early-close flapper can be replaced with standard flappers, it does not appear that early-close flappers were more likely than other flush valve mechanisms to produce high flush volumes or any other low-consumption toilet problem," the researchers write. "Double flushing, high volume flush and flapper leaks in toilets with early-close flappers occurred at a slightly lower rate than for all type or models of toilet."

We agree with the research's stance on alterability on one matter - replacement parts. Based on the findings, the wrong flappers could be mistakenly installed by homeowners. In follow-up phone surveys, 58 percent of homeowners involved in the rebate program had already replaced the flapper on their rebate toilets.

But with what? At 85 percent, the great majority has gone to a hardware store for a replacement flapper. As the researchers point out, hardware stores and home centers may not the best places to get the right part.

Who knows best? You do. Yet only 9 percent got a replacement flapper from their plumbers. We urge our readers to make their customers more aware of the engineering feat that produced 1.6-gpf toilets, and that not just any run-of-the-mill hardware special is required to keep it performing suitably.

Will a homeowner call a plumber just to replace a worn-out flapper? Probably not. But it's one more job your techs can check out as they make their regular rounds.

They can also advise customers to be leery of certain in-bowl cleaners. According to the Arizona research, 24 percent of those who knew they had flappers as flush valves used in-tank bowl cleaners. More specifically, halogenating agents generally use either "mixed halogenated methyl hydantions" or "calcium hydochlorite."