Many high-performing, water-saving fixtures and appliances are designed like straws, supplying only enough water to satisfy one’s thirst. But the pipes that bring that water into Americans’ homes are sized more like fire hoses.
Oversize plumbing pipes move water inefficiently, wasting money and increasing the risk of waterborne diseases. And water efficiency is especially important as climate change makes droughts more frequent and severe. Efforts to right-size plumbing pipes to match the intake of water-saving products are slowly gaining traction, but homeowners and designers of multiunit properties who want to use these more sustainable pipes need to demand them during the project design phase.
When the current method for sizing pipes to transport hot and cold water throughout the home was created in the 1940s, it was under the assumption that every fixture had to be able to support a line of people for the bathroom, like at a sports stadium at halftime, according to Christoph Lohr, a mechanical engineer specializing in plumbing systems and the vice president of technical services and research for the International Association of Plumbing and Mechanical Officials, a trade organization.
But even during a party at home, there won’t be a line for the kitchen sink, the shower, the bathtub, the laundry machine, the dishwasher and the toilets, with people using them over and over. In other words, most plumbing fixtures in the United States are designed to accommodate total flow rates far higher than they will realistically encounter.
Over the years, more homeowners have chosen water-saving devices, including those bearing the Environmental Protection Agency’s WaterSense label, which debuted in 2006. Products featuring the WaterSense label must be at least 20 percent more water-efficient than standard models, while performing as well or better. Low-flow toilets were among the first products to receive the WaterSense label, and are now commonplace. The current federal standard for toilets is 1.6 gallons per flush, compared with 5 gallons per flush before 1992.
Installing more efficient products works. Through the end of 2023, WaterSense helped Americans save a cumulative 8.7 trillion gallons of water and $207 billion in water and energy bills, according to an E.P.A. annual report.
To improve the efficiency of the pipes that supply those products, IAPMO developed the Water Demand Calculator, in conjunction with plumbing designers, plumbers, engineers and consultants. Simply enter data for a specific building or project into the calculator, and it will accurately predict the peak water demand, using three algorithms. Based on this data, a contractor or plumber can choose the pipe size best suited to the flow rate.
The Water Demand Calculator first appeared in the 2018 Uniform Plumbing Code and the 2017 Water Efficiency and Sanitation Standard, model codes that must be adopted by states or localities before they can be used. So far, 10 states and a handful of cities have adopted the calculator in their plumbing codes.
While most plumbers acknowledge they’re installing oversize pipes right now, they’re not inclined to make changes, especially when what they’re doing has been working.
Some of that reluctance stems from a lack of education, says Jessie Cannizzaro, president and master plumber at Milestone Plumbing in Wauwatosa, Wis., who sits on the National Association of the Remodeling Industry’s government affairs committee. Wisconsin includes the Water Demand Calculator in its plumbing code. But even across states that use the Water Demand Calculator, Ms. Cannizzaro says, plumbers aren’t necessarily taught to use it because codes and educational opportunities vary.
Steffi Becking, an associate director at the California benefit corporation 2050 Partners, is working to improve adoption of the calculator across the country. She and her team of consultants advise regulators on evidence-based changes to building codes and appliance standards.
In California, starting in 2021, Ms. Becking and Gary Klein, a water efficiency consultant, gathered case studies and data from two dozen buildings to present to the Department of Housing and Community Development and the Building Standards Commission, important regulators that coordinate updates to building codes in the state. “Gary and I started to set up meetings with people that serve on various committees, and started educating and asking what is the path for adoption in California,” Ms. Becking said.
The data sets they compiled showed that the plumbing code was overestimating measured peak flow rates by a factor of 10 or more on average. That convinced regulators in California to adopt the calculator in the plumbing code starting in 2023. “We don’t need a 10-to-1 safety margin for residential occupancies,” Mr. Klein said.
If those numbers aren’t enough to excite people in the plumbing industry to consider using the Water Demand Calculator, the financials might.
Some sustainability efforts cost more money at the outset, and builders need to consider the payback cost. But this is one of the few cases where builders will spend less money upfront, because smaller pipes mean lower transportation and labor costs.
John Lansing, a plumbing designer with P.A.E. Consulting Engineers in Portland, Ore., which includes the calculator in its codes, has been using the calculator in his projects. He found that by choosing right-size piping, he’s conserved water, increased water safety and saved his clients money.
Mr. Lansing recently used the calculator to complete a building of 276 units and saved $134,000 by reducing the service cost of installing the water meter.
“We don’t want to be installing pipes larger than we need,” Mr. Lansing said. “It’s like installing a 10-lane freeway out to a small town. Hypothetically, there could be a concert out there once every 10 years, but do we really want to design for that? Do we want to pay for that? The answer is no. Not only is it expensive, but there’s energy loss implications, reduces the water quality in the building. To a certain extent, it increases the public health risk.”
In pipes with slow or no water movement, bacteria like Legionella can proliferate and form biofilms, which can cause waterborne diseases. Legionella-associated outbreaks have increased over time and are the most common type of disease outbreak associated with drinking water, according to the Centers for Disease Control and Prevention.
“We’re not moving water fast enough, so the biofilm starts to grow, and once it grows, it’s really hard to get it out without using classic chemicals of some sort or using a high amount of turbulence,” said Patrick O’Neill, a master plumber and a plumbing instructor at Waukesha County Technical College in Pewaukee, Wis. He added that the Water Demand Calculator is an important tool against this hazard.
For homeowners and renters who cannot change their pipes, experts say there are still ways to improve water safety, conserve water and save money.
To reduce the risk of waterborne pathogens, Mr. O’Neill recommends flushing out plumbing once a year by removing aerators and then turning all the faucets on at the same time to run for five minutes. “You’ll create enough turbulence in that system to scrub most of your pipes clean,” he says.
And Mr. Lansing said one of the easiest ways to save money and conserve water is to install low-flow shower heads and faucets. “It’s just as easy as going to a hardware store,” he added.
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