Gray is the New Green

July 01, 2011
July/August 2011
A version of this article appears in the July/August 2011 issue of Home Energy Magazine.
Click here to read more articles about Water Efficiency

Projections are that by 2015, 36 U.S. states will have some degree of water shortage brought about by increasing population and shifting climate patterns. In California, a state already coping with severe water shortages (two water emergencies declared by former Governor Schwarzenegger in 2008 and 2009), the population is expected to double by 2050. It’s difficult to comprehend how it will be possible to accommodate the water needs of double the population when the needs of current residents can scarcely be met today. Our individual demand for water coupled with the needs of agriculture and energy production cannot be met without significant changes in how we use—and reuse—water.

If we don’t make these changes, we are facing tremendous competition for limited supply, especially in areas prone to drought. In any demand-supply situation, more consumers chasing after less water cannot help but increase the cost of that water. More importantly, this situation must dramatically affect the many areas of our lives that depend on water.


Table 1. Water Efficiency Improvements Can Cut Greenhouse Gas Emissions at Lower Cost
Figure 1. Estimated average U.S. household water usage.

How Much Water Do We Use?

Only about 10% of the water we use inside our homes is actually used as potable water—that is, used for kitchen and drinking purposes (see Figure 1). The average person uses upward of 100 gallons of water per day at home. This means that the United States as a whole, with a population of 311 million as of the 2010 census, uses 31 billion gallons of water a day, or 11.4 trillion gallons a year. And that’s for personal use. To produce the many items that a family of four uses every day takes up to 1,580 gallons of water. See Table 2 for more water usage statistics. (There’s a little bit of good news for beer drinkers. Of all the services and products that we consume every day, beer, believe it or not, is among the least water intensive—just a mere gallon of water for one beer!)

What Is Graywater and Is It Safe?

Graywater is the residual water from bathroom sinks, baths, showers, and washing machines. It includes water from HVAC condensate, and in public buildings, residual water from water fountains. Some, but not all, graywater can be safely reused. Although there are exceptions in some states and communities, water from kitchen sinks, dishwashers, and utility sinks generally cannot be reused, because it contains grease, food debris, and chemicals (when it comes from utility sinks). But much graywater can, depending on where you live, be reused for a number of purposes, including toilet flushing and subsoil irrigation. Up until recently, only fresh potable water could be used for these purposes.

Graywater has been safely used for countless generations to irrigate gardens and landscapes with water from dish washing, laundry, and bathing. Today, just under 2-million graywater systems are installed in California, and up to 8 million are installed nationwide. These systems provide graywater for reuse in its raw form—no filtering or treatment. No reported cases of illness have been associated with this basic reuse of graywater. Systems that filter the graywater and continuously disinfect it are even safer and much easier to use for flushing toilets; they can easily be connected to already-installed subsoil irrigation systems. Graywater, no matter what the source, must not come in contact with fresh water or be consumed by humans. It is, however, perfectly safe to be used for other purposes when it is properly treated and handled.

Graywater Solutions

Here are some choices for using graywater to save energy and water.

All-in-One Systems— Packaged or plug-and-play systems that are certified by third-party organizations such as the International Association of Plumbing and Mechanical Officers (IAPMO) provide the greatest level of confidence and security. Their seal of approval ensures that what you are purchasing has been tested and certified to work as designed. IAPMO works in concert with government and business to develop and implement appropriate plumbing codes in North America and throughout the world to ensure the safe use of water. Packaged systems meet many, if not all, local code requirements that address issues of public health and safety.

How do these systems work? For whole-house applications water is collected from the graywater sources in the home or commercial building, as described above. This water is filtered, disinfected, and stored in a tank. Most viruses, bacteria, and pathogens are neutralized in these systems by exposure to a proper treatment agent, such as chlorine or ultraviolet light. Although graywater is relatively clean, it can turn to black water within 24–72 hours if it is not used or disinfected. For that reason, some systems are equipped with automated chlorinators that minimally dose the water to keep it disinfected. The minimal dose is 0.5 to 1 ppm—usually less than the chlorine in the fresh-water supply to your home. As long as there is chlorine in the unit, it is highly likely that the water is being fully disinfected. (If you want to make certain, you can test the graywater in your toilet tank with a chlorine test strip, available in many stores and pool supply outlets. If tests indicate the presence of bacteria, you can adjust the chlorine setting in your system.) The treated water is then available for toilet flushing or subsoil irrigation, as permitted under local and state law. Contact your local building inspector or public health department to determine what is permitted in your community.

The installation of the packaged systems in existing homes requires the separation of graywater sources from fresh-water sources. This generally requires the services of a qualified professional. It is easiest to install systems for graywater capture and reuse when you are building a new home.

Fully integrated systems are pretty intelligent. They can automatically perform tasks that are beyond the scope of simpler systems. This relieves the homeowner of many tasks and makes the system itself much safer. A fully integrated system includes all the components you will need for daily operation. These components include but are not limited to

  • filters (including an external filter if the system is attached to a washing machine);
  • a chlorinator (provides automatic disinfection based on use, lasts up to three months on one filling, some models can automatically chlorinate when you’re on vacation);
  • a constant pressure pump (moves the treated water from tank to end use); and
  • an autofill valve (provides fresh water or rainwater to the system when there isn’t enough graywater in the tank).

Maintenance of these systems is pretty simple. Depending on use, and on the quality of the graywater, you may need to clean the filter every 7 to 14 days. Check the filter every 7 days in the first month or so to see whether the filter is clean, and adjust the cleaning schedule accordingly. Some systems will continue to disinfect the graywater when you are on vacation, but make sure (and instruct your customers to make sure) that there is adequate chlorine in the system before you leave on your trip. Check the chlorine at the same time as you set your water heater on vacation mode.

Simple Systems—Depending on where you live, a simple graywater reuse system can be as straightforward as redirecting the water from your washing machine to an area in your yard under a 2-inch cover of mulch, which protects people from direct contact with graywater and allows it to drain into areas where it is needed. Seek the help of a professional graywater system installer to accomplish this safely and effectively.

Some simple, or direct, systems collect the graywater and pump it out to irrigate the subsoil, but these systems must empty the storage tank within 24 hours, before the graywater turns to black water. Other systems can be installed under the sinks in bathrooms. Others may consist of an integrated unit, with the sink built on the top of the toilet tank to deliver the recovered water to flush the toilet. Although these systems are simple to install, the amount of recovered water may not be enough to meet the toilet-flushing demand.

Through a variety of these means, simple to sophisticated, a household can recover up to 45% of the graywater it generates—120 gallons or more of water per day, depending on the size of the family. This water can be treated and reused for toilet flushing and subsoil irrigation, as I explained above. Anywhere graywater is generated, it’s available to be recovered and reused, whether in homes, hotels, shelters, fitness centers, dorms, Laundromats, correctional facilities, or military barracks.

What Do Systems Cost?

There are a variety of systems available—from very simple homemade ones that cost less than $50 to under-the-sink or integrated toilet units for a few hundred dollars to highly sophisticated automated systems. All-in-one professional systems can range from $2,500 to $3,500 plus installation. The sophisticated systems can meet a household’s complete needs for toilet flushing and some subsoil irrigation.

All of these graywater systems provide savings in water and sewer fees. Many communities charge sewer fees based on the fresh water used. A 35–40% reduction in water use could well translate into a similar reduction in sewer fees. Depending on where you live, payback for a graywater system can be as little as three to four years, while the water savings also help to protect our limited and invaluable water supply. These systems can also help to save energy, as I explain below.

Graywater Reuse: Barriers and Possibilities

In some states the tremendous benefits of reusing graywater to flush toilets and irrigate the subsoil are widely accepted by state officials. This wide acceptance is reflected in codes that specify graywater reuse. Unfortunately, this is not the case in most states. The concern most often stated by those who oppose graywater use is that it endangers the public health. With almost 2 million nonpermitted systems in place in California (and 8 million nationwide), and no reported problems, it’s difficult to understand this concern. It is even more difficult to fathom given that modern systems filter and disinfect the graywater continuously to keep it safe. Most people who oppose the use of graywater are afraid that it may contain dangerous bacteria, but in fact we may well be at more risk from what the family pet leaves on the lawn than we are from bacteria in graywater.

How can home performance professionals, and graywater system installers and users, encourage the wider adoption of graywater reuse? Here are some ideas to consider.

Businesses and water utilities can provide information on graywater reuse to homeowners through seminars, meetings, web sites, and literature. This information should address safety and health concerns, describe the various kinds of systems, and outline the appropriate uses for graywater.

States and local governments can establish standards and guidelines for the safe reuse of graywater—standards and guidelines that make sense to homeowners.

Code officials can require that graywater lines be marked with purple-and-white tape. The color purple is commonly used to identify water lines that contain nonpotable water. An additional safeguard would be to color the graywater itself blue with a nontoxic dye, to indicate that it is nonpotable water.

In anticipation of full code approval for graywater reuse in homes for toilet flushing (currently approved in some states), states should require all new development and retrofits to install appropriate piping to accommodate reuse of graywater.


Table 2: Water Consumed to Provide Selected Products

Table 2: Water Consumed to Provide Selected Products
Table 3: Water Consumed by Various Energy Sources

The Water/Energy Nexus

Since we as a society generally pay more attention to energy conservation than to water conservation, perhaps we should consider how using graywater saves energy. We might even see a reason to provide incentives for water conservation in the same way and at the same level as we do for renewable energy.

It takes a massive amount of water to support the average family for personal use and to grow, raise, or produce all of the food, products, and services we consume and use every day. We need water to generate energy, and we need energy to treat and move the water to where people use it. For example, 2–3% of the total energy consumed in California is used simply to move water from Northern to Southern California, as part of the California State Water Project.

Water and energy are inextricably linked in a symbiotic relationship in which each needs the other to fulfill the demands of our citizens and commerce. Projected increases in energy use will lead to greater use of water to generate electricity (unless we move to less water-intensive energy generation); and population growth increases demand for water, which in turn requires more energy to get it to the people, and so on.

Water is needed to generate energy, but some energy sources are more water intensive than others. While reducing energy use continues to be challenging, we can use less water-intensive sources to generate that energy. Table 3 shows how much water is used to produce each kWh of energy from seven different energy sources. There are some significant surprises, most notably in the case of hydropower, which can use more than 18 gallons of water to generate 1 kWh. Renewable-energy sources (wind and solar) use almost no water.

Depending on where you live and how your water is sourced, the amount of energy required to provide water can also vary dramatically. Data available from Portland, Oregon, show that 5 times more energy is needed to extract water from ground storage than is needed to get it from the Bull Run Reservoir, which supplies the city. In San Diego, energy intensity of water sources varies considerably. The energy needed to provide 100 gallons of water is 0.6 kWh from the Colorado River Aqueduct, 1 kWh from the State Water Project, 0.18 kWh from groundwater, and 0.15 kWh from reclaimed water.

Saving water cuts down on the energy we use, and saving energy cuts down on the water needed to generate the energy. Water conservation can save energy and reduce CO2 emissions at less cost than direct energy conservation (see Table 1).

Reductions in water use save energy, and those energy savings can really add up. In 1992, the Santa Clara Valley Water District implemented a water efficiency program. The program included free home water audits, low-flow showerheads and faucet aerators, and rebates for water-efficient landscaping. As of the end of fiscal year 2006, the water district had realized a savings of 1.42 billion kWh of energy (see Figure 2).


Case Study: Santa Clara Valley Water District

Case Study: Santa Clara Valley Water DistrictFigure 2. Energy savings from the Santa Clara Valley Water Efficiency Program 1992-2006.

Case Study: Santa Clara Valley Water District Source: Santa Clara Valley Water District, 2007. From Watts To Water, Santa Clara, California

learn more

For examples of simple graywater use systems, go to

For more on undercounter or vanity systems, go to

To learn more about integrated toilet tank units, go to

And to learn more about automated graywater reuse systems, go to

You can also go to my company’s web site,, to learn more about water- and energy-saving options for you and your customers. To learn more about a one-two flush kit, go to

For information on the best, high-performance toilet models on the market, go to the web site of the Alliance for Water Efficiency, at There you will find the results of the alliance’s MaP (maximum performance) program, which tests toilet performance and efficiency.

In addition to saving water, and reducing the energy needed to get the water to your home or business, reusing graywater provides another benefit—most graywater is warm water. The latent heat in it can be extracted through a simple heat exchanger on the sewer or septic waste line to preheat your hot water by up to 30ºF—for free (see “Drain Water Heat Recovery Devices,” HE May/June ’08, p. 34). When this energy is stored in the graywater tank and is allowed to radiate into your home (if the storage tank is installed within the building envelope), energy that was previously lost can also be made available to heat your home. Conservatively speaking, 1,000 kWh of energy or more can be recovered each year by recovering the waste heat in the graywater. This is one-third to one-half of what a solar hot water or solar-electric system can provide, but at a much lower price.

The Huge Promise of Water Reuse

Because of the sheer volume of graywater generated annually by us as individuals (39 gallons per person per day; 530 billion gallons per year in California; 4,300 billion gallons per year in the United States), even small changes can have a dramatic effect on the water and energy that we use. But the amount of graywater that we generate is so enormous that it is difficult to truly fathom. Imagine a 10-inch pipeline that would stretch to the sun and back. Now imagine that pipeline filled with graywater. That is the amount of graywater that we generate in the United States per year. Even a 10% recovery of graywater in California would yield approximately 53 billion gallons of water saved. On a local level, annual savings for a family of four could be over 20,000 gallons; a 100-room hotel could save 1.2 million gallons, a health club 600,000 gallons, a Laundromat 300,000 gallons, a correctional facility with 1,000 inmates 2.7 million gallons, and a town of 10,000 residents over 56 million gallons.

In addition to saving water and energy, reducing our use of water effectively increases the capacity of municipalities to meet the demands of ongoing population growth without the need to upgrade the water infrastructure. This can save government and citizens hundreds of millions, or even billions, of dollars.

Small Steps

Start small, conserve. Buy and install for your customers who want them new low-flow showerheads and low-flow faucets. Upgrade toilets with a one-two flush kit to reduce water used per flush, or replace older toilets with new high-performance, low-flow models.

When buying new appliances like dishwashers or washing machines, buy models that are water efficient (look for the Energy Star label, of course). Many utilities offer incentives in the form of rebates to encourage their customers to purchase these models.

Reuse your graywater—it’s easy and safe. Let your public officials know where you stand. Submit a permit application for a graywater system. You may well be surprised when you discover how many people want to help. Learn how to install graywater systems and make this service something you offer your customers. It will save them money and distinguish your company from your competition. Remember: Reusing graywater is not only the green thing to do for the environment and our future generations—it can be “green” for your wallet, too.

Peter Byrne is the owner of Setanta Energy & Water.

This article is part of a series sponsored by Home Performance with Energy Star, jointly managed by the U.S. Department of Energy and Environmental Protection Agency. The opinions, views and ideas expressed within this article are those of the author and do not necessarily reflect the official policy or position of any agency of the U.S. government.

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