When it comes to testing toilets, it turns out the appropriate substitute for human feces is miso paste. That’s what EPA uses to ensure that commodes earning its WaterSense efficiency label flush effectively.
To earn the label, tank-type toilets currently must use 1.28 gallons or less of water per flush while eliminating 350 grams of miso paste, along with toilet paper.
That may be news to President Trump, who last week complained that low-flow toilets were not getting the job done, so "people are flushing toilets 10 times, 15 times, as opposed to once."
"They end up using more water," he said, before suggesting that EPA is looking "very strongly" at "opening up the standard."
Exactly what the president meant is unclear. But his comments do highlight an ongoing debate between municipalities and the plumbing industry over whether WaterSense should tighten its criteria to ensure more human waste goes with the flow.
WaterSense is not a regulatory program but rather a voluntary labeling initiative meant to aid consumers looking for options. Federally mandated maximum volumes of 1.6 gallons per flush were codified by Congress in 1992, and the Department of Energy is responsible for those regulations.
EPA spokesman Michael Abboud said the agency is working with "all federal partners" to review how programs under the federal energy management plan interact "to ensure American consumers have more choice when purchasing water products."
The WaterSense program this year studied whether to reopen its standards for toilets, along with faucets, showerheads, flushing urinals and weather-based irrigation controllers, after Congress asked for reevaluation of specifications set prior to 2012.
The miso paste ‘performance score’
The agency will decide which standards — if any — to reconsider by the end of the year, and the effort has sparked some debate over what a flush should be able to accomplish.
While federally mandated water efficiency standards don’t take flush success into account, EPA’s WaterSense program, meant to help consumers make decisions, does.
WaterSense’s lead engineer, Stephanie Tanner, explained in a webinar this spring that the program’s label is meant to help consumers interested in water efficient products find those that perform well and take the plunge.
"The people we are targeting are early-ish adopters, but not the earliest adopters," she said. "They are looking to make a change in their products or looking for efficiency or better performance but aren’t quite sure how to do that, and we use the label to help them identify the product they are interested in and make that positive choice in the marketplace."
In other words, no one wants a toilet that uses so little water it needs to be flushed multiple times.
Enter the miso paste "performance score." The traditional Japanese seasoning, described by WaterSense documents as "a test media having similar physical properties to human waste," is actually the industry-accepted stand-in for feces. It was selected after years of trying other options that once included pingpong balls, said Ed Osann, director of national water use efficiency at the Natural Resources Defense Council.
Already, there are a number of WaterSense-labeled products on the market that exceed its 350-gram clearance requirement. Of the 3,400 toilet models that have earned the label, nearly two-thirds can clear 600 grams or greater, and more than half of those achieved the "maximum allowable score of 1,000 grams."
Because of this, some water utilities are asking EPA to make the criteria more selective, arguing that doing so will ensure the program doesn’t become obsolete.
Georgia is one of six states that already require toilets to use less water than WaterSense. The standard there is 1.28 gallons per flush, and the water utility serving greater Atlanta wants EPA to lower WaterSense specifications to 1.1 gallons or less.
The Metropolitan North Georgia Water Planning District said it’s seen a small but growing percentage of customers using toilets that achieve that level of water efficiency, and some that use as little as 0.8 gallon per flush.
"Based on customer calls that come into the district’s toilet rebate call center, we generally hear positive feedback and extremely few complaints from customers," the utility wrote EPA this spring. "To reduce even these few complaints, we support revising the performance criteria to require tank-type toilets to clear a larger quantity of waste and/or toilet paper."
What’s in a flush?
But Plumbing Manufacturers International opposes that idea and says waste elimination is not the No. 1 reason people flush more than once. It’s actually No. 2.
That’s according to a 1999 customer survey done by the Metropolitan Water District of Southern California that examined "the root causes of double flushing."
Clearing "bulk waste" was only a factor 21% of the time. The leading cause of extra flushes, coming in at 47%, was "bowl cleanliness."
"Any requirement above 350 grams does not necessarily make the extraction of solid waste more efficient or effective, but instead may encourage manufacturers to focus unduly on waste extraction," the trade group wrote EPA this spring.
Bowl cleanliness and "light waste" removal require "fluid dynamic design considerations" on commodes, PMI wrote, meaning "increasing the gram requirement could result in products that are less effective in meeting consumer needs, not more effective."
Stan Meiburg, who served at EPA for 39 years, most recently as acting deputy administrator, noted that municipalities stand to gain a lot from more effective, efficient toilets because saving water saves energy.
WaterSense has saved 2.7 trillion gallons of water since 2006, which translates into $63 billion in consumer savings on water and energy bills, according to EPA.
Plumbing manufacturers, on the other hand, might have to completely redesign their products to achieve WaterSense’s goals.
"If you just use a toilet that’s originally designed at 7 gallons and try to make it work on 1.6, sure it won’t work as well," Meiburg said. "But when you redesign the toilets and the trap ways and the flush valve where the water leaves the tank, you redesign it to work better on less water, and it does."
Osann, at NRDC, said that while he’s sympathetic to the logic that "there are many reasons people flush more than once," the plumbing industry is likely just trying to maintain the status quo.
He praised the industry for making so many strides since the 1990s and said the progress is one reason "the president’s comments last week just don’t ring true."
"If you think about it, the bowl brush and the plunger were invented long before the 1.28-gallon toilet," he said.
Correction: An earlier version of this article listed the Georgia standard as 1.2 gallons per flush. It’s 1.28 gallons per flush.