Hot Water: Why Plumbing Technologies and System Designs Matter

January 31, 2015
March/April 2015
This online-only article is a supplement to the March/April 2015 print edition of Home Energy Magazine.
Click here to read more articles about Hot Water

The average home in the United States makes at least 2,000 annual demands for hot water. And that’s very conservative. A more-likely demand value exceeds 4,000. Couple those demands with an average wait time for hot water at the master bath showerhead in single-family homes that is, according to an informal web poll performed by the National Resources Defense Council, more than 70 seconds. That’s a lot of water down the drain waiting for hot water! Even with a highly efficient showerhead, that’s 2.3 gallons—for just one hot-water demand event!

The beautiful, dry, Arizona landscape showcases our need to be careful with our water use.

Per Demand Average Wasted Water And Tme Waiting for Hot Water Without DCP

Per Demand Average Wasted Water And Tme Waiting for Hot Water Without DCP
Figure 1. This chart shows the per-demand daily averages of wasted water (cups) and wasted time (seconds) in the homes before DCPs were installed.

Per Demand Average Wasted Water And Tme Waiting for Hot Water With DCP

Per Demand Average Wasted Water And Tme Waiting for Hot Water With DCP
Figure 2. This is the companion chart, with same scale as above, showing per-demand daily averages after DCPs were installed.

In today’s environment of regional water scarcity, more homeowners are becoming aware that conserving water, energy, and dollars makes good sense. The price of water and energy is rising in many communities, and builders are challenged to meet new, more-stringent plumbing codes that help make homes more affordable to live in and sustainable for current and future homeowners.

Efforts such as the EPA WaterSense program, and that of the Cochise Water Project, in Arizona, are taking us in the right direction—using less water and less energy in our daily lives.


EPA created the WaterSense program to help millions of homeowners save water and energy, and to help communities in areas where water shortages of recent years are beginning to look like the new normal.

This program helps consumers make smart water choices that save money, time, and water-heating energy without compromising performance. In order to be certified, products and services must be at least 20% more efficient than typical hot-water systems. An example of a typical measure used to reach that goal includes installing a WaterSense-labeled faucet aerator. This alone could save a household 11,000 gallons over the life of the faucet.

The Cochise Water Project

During 2011–12, the Cochise Water Project (TCWP), a nonprofit public-private partnership, began to address how to reduce wasted water in homes in Sierra Vista, Arizona. I served as first chair of the Technical Advisory Committee for the TCWP board of directors from 2012 through 2014. The sole mission of TCWP is to reduce water use. Of the six projects undertaken by TCWP to date, two targeted hot water. This is a report on one hot-water project: the installation of demand-controlled pumps (DCPs) in existing homes in the Sierra Vista area. (See “How a Demand-Controlled Pump Works.”)

In 2013, TCWP installed more than 130 DCPs in existing homes without recirculation pumps of any kind. In early 2014, homeowners were asked to record wasted water and wasted time at their kitchen sink and at a fixture in their master bathroom—using a stopwatch, a small cooking pot, and a measuring cup. Of the 130 homes, more than 30 provided TCWP with sets of data on wasted water and wasted time before and after DCP installation. These data allowed TCWP to analyze the impacts of the DCP on wasted water, wasted energy, and wasted time. Figure 1 and Figure 2 show what was learned.

How a Demand-Controlled Pump Works
With a demand-controlled pump, the homeowner controls when a hot-water demand is made. Pushing a hard-wired or wireless transmitter button or a motion sensor sends a signal to tell the pump to operate.  The pump is normally installed at the hot-water fixture that is farthest from the water heater, using the hot and cold stub-outs to form a loop from-to the water heater. The pump’s thermistor senses the temperature of the water at the faucet. If it falls below 105°F, the pump notes the temperature and begins to pull hot water from the water heater, sending the displaced water back to the water heater via the cold-line plumbing.  Once the temperature of the water at the pump increases by about 6–7°F, the pump shuts off. Hot water is now about 2–5 feet from where it will be used.

Figure 1 shows the average wasted water (in cups) and wasted time (in seconds) in homes before the DCPs were installed. The data were transformed into four daily hot-water demand events—three at the kitchen sink, and one in the master bath—and averages were calculated. The data points represent the per-demand daily averages for all homes. Figure 2, with same scale as Figure 1 shows the per-demand daily averages with a DCP installed.

The results were dramatic! Here are some of the highlights of the analysis, including the results of occupant surveys:

  • With the DCP activated, wasted water, energy, and time are reduced by a factor of 5.
  • When considering these same reductions from a water–energy nexus perspective, going from cradle to grave—from a watershed to and through a home and then on to sewage disposal—the factor increases to 6!
  • On average in the United States, it takes 37 times more energy to heat a given volume of water for a shower than it does to move that same water cradle-to-grave.
  • When surveyed, all of the homeowners who installed DCPs via the TCWP project said they would do it again.
  • When asked what they liked best about their DCP, they all said, “the convenience.” This was a surprising outcome—the homeowner’s increased convenience trumped the water and energy savings.

learn more

Go to for more on the Natural Resource Defense Council’s shower hot-water wait time poll.

Find out more on EPA’s WaterSense project.

Get more on the Cochise Water Project, including a list of public and private stakeholders.

Get information about the ACT D’MAND demand pump systems.

Read more on Reality LLC.

To my knowledge only a DCP provides the plumbing technology that is Uniform Plumbing Code (UPC)-compliant for existing homes for preventing hot- and cold-water interconnections. When you consider that there are 76 million owner-occupied homes in the United States, a huge opportunity exists to dramatically reduce wasted water, energy, and time. The TCWP experience shows that collaboration and cooperation among municipalities, water agencies, and energy providers can save energy and water, and create a better life for customers. This is low-hanging fruit.

The key is to meet the hot-water delivery standard of WaterSense by using whatever solutions are appropriate. Let technology and smart plumbing design work for the betterment of all.

Water and energy savings are crucial if we are going to live in our homes in a way that is sustainable. But there is something to be said for convenience when waiting for hot water. Just ask 130+ homeowners in the Sierra Vista area.

Dave Grieshop is the managing partner of Reality LLC, in Sierra Vista, Arizona.

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