Passive design significantly reduces indoor water use, pilot program demonstrates

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The average U.S. family uses 320 gallons of water per day, about 70% of it indoors, according to the Environmental Protection Agency. What if that figure could drop dramatically – with little to no impact on consumers?

Programs such as tiered pricing and smart water meters help drive conservation. But the 50L Home Coalition, a project of the World Business Council for Sustainable Development, is adopting a different approach: energy-efficient and well-designed appliances and more effective consumables like laundry and dishwashing detergents.

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The 50L coalition seeks to help urban residences achieve an average of 50 liters (about 13 gallons) of water consumption per person per day. The vision is to make those 50 liters feel like 500 liters. This way, consumers will save water without compromising comfort and quality of life.

This renewed focus on consumers is expected to help adoption.

“50L starts on the premise that water efficiency scales fastest when it improves everyday living,” said Neil Patel, manager of the coalition. “Homes work better, routines become simpler, and lower water use becomes the natural outcome of better design, not behavioral effort or sacrifice.”

Pilot study and results

To test the feasibility of its premise, the coalition conducted a pilot project in water-stressed Greater Los Angeles.

The team recruited residents from 31 homes and retrofitted 15 of the houses with water- and energy-saving appliances, fixtures, and consumer products from partner companies such as Electrolux, Procter & Gamble, Ikea, and Kohler.

Throughout the process, the study evaluated residents’ perceptions and behaviors at every point of use in the home to understand water and energy consumption.

After two years, retrofitted households used 21 gallons of water (79 liters) per person per day on average, which is 56% less than the official LA average of 48 gallons. Daily hot water usage at the kitchen sink dropped by 49%, a number similar to that reported for laundry use. Meanwhile, control homes maintained an average of about 100 liters per person per day and did not record any statistically significant changes in consumption throughout the pilot phase.

The results offer “a compelling proof point for utilities, policymakers, manufacturers, and the building industry that indoor water efficiency provides reliable, year-round savings that complement outdoor conservation programs, reduce energy use and emissions associated with hot water, and yield a positive return on investment,” Patel said.

Because the focus was on performance-driven passive engineering and design, participants were not asked to take shorter showers, flush less often, or make sacrifices to conserve water. This contrasts with traditional water demand management that relies on behavioral restrictions or conservation messaging through tiered water pricing, drought restrictions, and smart water meters.

What savings might mean for utilities

Hot water savings jointly benefit power and water utilities, a co-benefit that outdoor conservation alone can’t provide, Patel pointed out.

Benefits to utilities from reduced water consumption add up quickly. Showers, washing machines, dishwashers, and toilets “run consistently, so the yield to a utility is steady and predictable, unlike outdoor conservation, which is weather dependent and requires the customer to commit to ongoing landscape maintenance,” Patel said. Utilities have the potential to reallocate water that customers save.

In addition, “demand reduction lowers utility operations and maintenance costs across the whole system,” Patel said. “Every liter saved indoors is a liter the utility doesn’t have to source, treat, pump, distribute, collect as wastewater, and treat again on the back end.”

This approach can reduce chemical and energy spending, decrease wear on pumps and pipes, and help defer replacement capital expenditure costs, Patel added.

“In cities that run combined sewer systems where wastewater and stormwater share the same pipes, lowering baseline indoor wastewater volume gives the system more headroom during storms, reducing combined sewer overflow events,” Patel said.

Christoph Lohr, P.E., vice president of technical services and research at the International Association of Plumbing and Mechanical Officials, encourages a holistic view of water conservation. Policymakers, for example, need to factor in the downstream consumption of treated wastewater as well.

Phoenix is doing its part by diverting treated wastewater as cooling material for the Palo Verde Generating Station, a nuclear power plant 55 miles to the west. “So when we consider reducing consumption, it’s a good idea to really think through the whole system,” Lohr said. “Otherwise you might end up with unintended consequences.”

For the long term, Patel sees demand reduction as complementing customer assistance programs for bill relief and affordability.

“Rebate programs that reliably reduce indoor water use are a longer-term solution to affordability challenges for low-income households,” he said. “This is particularly impactful where programs can be split between the energy and water utility due to the joint savings opportunity.”

Plumbing changes ahead?

Utilities might also have to evaluate how and which kinds of water meters they use to measure water consumption, Lohr said. Oversized water meters lead to lost revenue for utilities because every water meter has a minimum flow rate that it can measure. Leaks and other circumstances with low flow rates might not be measured at all. To accurately assess water consumption and corresponding pricing, water meters should not be larger than needed.

As appliances become more efficient and as consumers use less water, pipe sizing will have to change too, Lohr said. Even today, standard practice design greatly exceeds actual peak flow rates, which means pipes are too large for the water flow they need to handle.

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When pipes are larger than they need to be, water flows through more slowly, adversely affecting water pressure. It also increases the chances for pathogen growth, which is especially problematic for immunocompromised people. In addition, oversized pipes mean a higher volume of water is displaced at a slower rate before the water gets hot enough for showers.

The IAPMO encourages use of its water demand calculator to right-size pipes. Given the results of the LA pilot, the momentum to adopt smaller piping and water meters is likely to increase.

“Just by delivering hot water faster and more efficiently with the right-size pipe systems, you’re looking at an outdoor hot tub’s worth of savings in an apartment or home every year,” Lohr said.

What’s next

Implementing the program at scale is likely to prove challenging, said Maureen Erbeznik, senior adviser for water innovation at USGBC California, a regional partner of the U.S. Green Building Council. The fragmented water utilities industry will need to be addressed as a whole, as will consumer behavior. “The paradox of ‘cheap water’ is probably the biggest obstacle,” Erbeznik said.

Scaling can happen in smaller steps. For example, the 50L coalition’s immediate goal is to make 80-liter (21-gallon) living the first “scale-ready” step toward 50 liters, Patel said.

One of the many encouraging results of the LA pilot is that it shows room for improvement in residential water conservation programs. Training, education, and further innovation in design will also help.

“One of the beliefs is that (minimizing) indoor water use is done, that we have hit demand hardening, but I believe we still have room for improvement,” Erbeznik said.