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Domestic Water Conservation:
Greywater, Rainwater and Other Innovations

(Released February 2004)

  by Bryan Flowers  


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Approximately 26 billion gallons of water are used every day in the United States alone. According to the United States Geological Survey, the average American uses between 80 and 100 gallons of water daily.1

As the population of the United States, and the rest of the world, continues to grow, water and other natural resources are consumed at an increasing rate. As water resources are depleted, overuse of existing supplies often occurs. Water management has traditionally involved the manipulation of water supplies, rather than focusing on altering water demand. This has been done through dams, water conveyance structures and the location and development of new supplies. However these methods will continually face economic, ecological and hydrological concerns.

Hydrology dictates the replenishment of water supplies, though it does not follow political boundaries. This creates global issues over water rights and water resources that can potentially escalate to military confrontations. Ecological and environmental concerns also arise with the overuse of water supplies. For example, lowered surface water supplies can damage habitats for aquatic life, and the over pumping of groundwater resources can lead to land subsidence.2

The effects of land subsidence are apparent in many areas, including Houston, Texas and the San Joaquin Valley in California. A long history of groundwater use in Houston has led to increased flood hazards and affected the nearby Galveston Bay Estuary. In the San Joaquin Valley, large amounts of groundwater have been pumped to sustain extremely productive crops. This agricultural water use has resulted in one of the largest human alterations of the Earth's surface.3

Approximate maximum subsidence location
Land Subsidence in the San Joaquin Valley, California

On a scale that affects homeowners more directly, shortages in water supplies can result in building moratoriums. Such moratoriums have been enacted in Frederick, Maryland and in the community of Hat Island in Washington. Hat Island was only able to overcome this moratorium by constructing a costly reverse osmosis plant for the desalination of sea water.

Municipalities and water companies are also often required to enforce water use restrictions on their users or customers, especially in months of drought. Moratoriums may be in direct conflict with population growth and can create problems and price increases within the construction industry.4 Homeowners may object to water restrictions, as it dictates how they can care for their property.

Finding new supplies can be costly, both in time and money, and is never guaranteed. One potential solution to these issues is lowering domestic water demand year round. This can avoid depletion of water supplies, leaving more plentiful supplies during times of drought, and can possibly eliminate the need for water use restrictions and ensure adequate supplies for additional homes. This can be accomplished in several ways, varying greatly in terms of complexity, cost, and personal effort. No method is without its problems, but each is a way to help alleviate water shortage concerns.

Water conservation is the responsibility of both water users and suppliers. Both can employ numerous methods to preserve water supplies. There are many advanced techniques and devices to help conserve water, such as greywater reuse, rainwater collection, water-conserving landscaping and irrigation practices, the installation of low-flow fixtures and appliances, and proper swimming pool maintenance. Water users can also conserve water through some common-sense strategies in the home. These are known as "Wise Water Use" methods and include taking shorter showers, taking baths instead of showers, running only full loads of laundry and dishes, and being prompt in repairing leaky plumbing. Methods undertaken by the water supplier often include the aforementioned water use restrictions, vigilant water metering, and increased awareness of water distribution system maintenance needs.

Water User Responsibilities

To avoid additional water use charges or restrictions, the task of water conservation falls to the users themselves. Conservation methods exist for both internal and external water use.

rainharvesting pie chart


The first method of water conservation, and perhaps the one requiring the most investment and equipment on the part of homeowners, is greywater recycling. Greywater, or sullage, recycling is defined as the reuse of water from the sinks, showers, washing machine and dishwasher in a home.5 Greywater currently contributes 75% of total wastewater flow to domestic sewers.6

Most recycling systems involve a diverter valve which separates greywater and blackwater. Blackwater is sent to a conventional wastewater treatment system. Greywater is run through a filter, typically a sand filter, to remove any organic matter, then relocated on site either to be treated by a separate process or used as-is.7 Common treatments include chlorination or iodine for disinfection 8 Biological treatment systems are also available, including constructed wetlands involving water hyacinths or other plants for disinfection with metal ions.9 Aquatic plants remove pollutants both by directly absorbing them into their tissue and by providing a suitable environment for bacteria to transform pollutants and reduce their concentrations.

greywater culvert detail


Untreated greywater can be used for several water consuming activities, most notably outdoor washing and irrigation. Some studies have shown no adverse effects on lawns or ornamental gardens where greywater has been used for irrigation.10 In fact, there is even evidence that nutrients found in sullage will promote better plant growth than typical chlorinated municipal water. However, it is recommended that the use of harsh detergents or cleansers, such as boron or bleaches, be discontinued if greywater is to be used for irrigation. Also, greywater use should be avoided on acid-loving plants, as most greywater is slightly alkaline due to soaps and detergents present. It is also possible that extended greywater use may elevate sodium levels in soils, causing drainage problems and potential damage to plants.11

The major concern with greywater reuse is the quality of the water. It is imperative for greywater to be separated from blackwater; even then, pathogenic microorganisms can still be found in greywater. Therefore treatment of greywater before its reuse may be necessary, and contact with humans is not recommended due to public health concerns.12 It is also not recommended for greywater to be stored for long periods of time because it can create breeding grounds for bacteria and pathogens, as well as foul odors.13 If water from kitchen sinks is used, it may be necessary to include grease traps in the recycling system, and the filter selected must be able to separate out food particles.

Because of these water quality concerns, many areas do not permit wastewater reuse in the home. In Australia, domestic wastewater reuse is not permitted, despite support from the community.14 Another major concern is the installation costs of the systems. Filters alone can cost approximately $1000 US.15

Another method of domestic water conservation is the installation of water-efficient appliances and low-flow plumbing fixtures. The most common devices are low-flush toilets, faucet aerators, low-flow showerheads, and reduced water-use washing machines and dishwashers.16 Faucet aerators alone can cut water flow through that faucet by 50%.17 Faucet aerators mix air with the water which serves to reduce splashing and cuts the flow.18

faucet aerater


A study of household water use conducted in the Netherlands examined the difference of per capita consumption before and after water-efficient appliances had been installed. The overall daily per person consumption declined 4 liters, due mostly to the appliances, rather than changes in water use habits.19 Another study, located in Seattle, Washington, demonstrated that the most effective water-efficient items were toilets, washing machines and faucet aerators. Retrofitting a home with these devices accounted for an 18 gpcd decrease in water use.20 Installation of these appliances can cut a community's water consumption by 20%21 .

A major concern with this method is the user cost for the installation of such devices. A survey of home builders and municipal officials indicated that only 22% of these individuals felt that homebuyers would pay over $100 U.S. to have water-saving fixtures in their homes.22 One possible remedy is the creation of a trust that could subsidize the installation of the appliance and fixtures. One such Trust has been proposed in the United Kingdom, but has yet to be put in place. Funding could come from fines on water companies that are not vigilant on leak detection, or from an increase in water abstraction charges.23

In some areas of the United States, rebates are offered to home builders if they equip new homes with water-saving appliances.24 It was estimated in California, that if only 2% of households installed these devices, savings alone could pay for the installation of the devices in all households.25

Finally, internal Wise Water Use strategies involve changes in water use habits, including bathing and household cleaning. However, personal water use habits can be hard to change. A more effective Wise Water Use method is vigilance with leak detection and repair. A dripping faucet can leak up to 200 liters per day, while a leaking toilet can account for 16,000 liters per year.26 More practical methods can save additional water, though they may require considerably more investment both in time and money.

External water conservation is just as important as internal, as in some areas up to 50% of homeowner water use may be outdoors.27 The highest end of the spectrum is encountered in warmer regions, where more water is used for lawn maintenance and where a greater number of swimming pools can be found.

Lawn care accounts for about 32% of residential outdoor water use. Up to 180 gallons can be needed each time a lawn is watered, which occurs several times throughout the growing season.28 One way to eliminate this need is to limit the amount of grass by planting trees, shrubs or ground cover which absorb much more rainfall and require less maintenance than turf grass.29 Where grass is planted, lawn watering can be limited to evening or early morning hours. Wind and temperatures are low at these times, lowering the amount of water loss through evaporation. Placing mulch around plantings can also reduce water evaporation up to 70%.30 Also, lawns mowed shorter than 2 centimeters are likely to lose more water to evaporation.31

There is also a landscaping technique known as xeriscaping, which is most prevalent in warmer climates, such as the Southern and Western United States. The term xeriscaping is derived from the Greek word "xeric," meaning dry. It involves the use of xeric plants in landscaping and is defined as "a landscape method that maximizes the conservation of water by using site-appropriate plants and efficient water use techniques."32 It has been shown that a properly maintained xeriscape may only need about one-third the water of a turf-based landscape.33 One aspect of this technique involves placing plants together in groups based on their drought tolerance and irrigation needs. This allows for only certain areas of a yard to be watered when a need for water is indicated.34 Studies show that xeriscaping can contribute to a 20% reduction in water consumption when coupled with a few other conservation methods.35 Verbena, geraniums, dianthus and succulents are examples of plants used in water-conserving landscapes. When combined with aesthetic elements, such as gravel walkways or mulching, an attractive yet water efficient landscape can be produced.36

Another way to lower demand on municipal supplies is the collection of rainwater. This can potentially save 50% of domestic water consumption. This water can be used not only for garden and lawn watering, but even for toilet flushing and clothes washing. Rainwater is very soft and free of chlorine, which makes it acceptable for these uses. In order to maintain the quality of water at acceptable levels, organic matter must be filtered out. Incoming rainwater introduces oxygen into the storage systems, and when the water is kept aerobic in this way foul odors do not develop.37

Proper swimming pool maintenance can also help to lower water demand. Evaporation is the largest cause of water loss in swimming pools. The average pool can lose up to one inch of water per week through evaporation.38 This can be anywhere from 720 to 3,000 gallons a month.39 In sunny areas, such as California, a pool can even lose its entire volume of water within a year.40 The best way to limit water loss by evaporation is through a pool cover, which can reduce evaporation by up to 95%.41 Windbreaks around pools will help reduce evaporation on breezy days.42

Significant water is also lost from pools through splashing. This rate is about 25% that of evaporation.43 Ways to lower losses from splashing include diving board removal and lowering the water level in the pool. New ice compensating techniques winterize pools without requiring a drop in the water level, therefore eliminating the need to drain the pool water. However, if draining is necessary, neutralizing the acids and restricting chemical use prior to draining allows the water to be used for constructive purposes, such as watering the lawn.

Water Supplier Responsibilities

Maintenance of water distribution systems is the most effective method of water conservation employed by water suppliers. This is done by leak detection and repair, as well as control of pressure oscillations in water supply networks. Proper control of the pressure alone can lower annual water use by 3-6%.44

Water use restrictions place limits on household water use. These are decided by municipalities or water suppliers and dictate both when and how households may use their water. These are most often applied to external water use. Examples are limiting lawn watering to even numbered houses on a street on even numbered days of the month, banning car washing, and limiting use of outdoor fountains. Homeowners generally disagree with these methods, which are perceived as personal intrusions.

Water metering involves strict measurement of the water use of each household. This is often coupled with an increased charge for a volume of water used, as metering itself will not lower water use. Price increases are not without concerns. Middle class homes might begin to feel a pinch, and working class homes may reduce their water consumption to unhealthy levels to avoid costs. Increasing water use rates solely for certain homes, for example homes with swimming pools or those with garden sprinklers, would not have much affect on total municipal water consumption.45

Public Acceptance

Despite each individual method having its own specific concerns, some concerns are shared by multiple methods, most notably costs and changing of personal habits. However, public opinion is a major hurdle for every water conservation strategy. Public acceptance of these methods is very important, yet many public education efforts have not succeeded.46 The process of selling these technologies and methods to the public has become a major policy issue.47 Encouraging the public to conserve water in times of shortage is possible, but educating them to conserve water when there is no crisis has become difficult.48 The most successful efforts have been the creation of model homes, or other publicly viewable projects, employing water conservation technologies.

One of these homes is Casa del Agua in Tucson, Arizona. This house began as an existing residence in 1983 and was retrofitted to acquire operational data on residential water use. Modifications included altering landscaping and the rooftop to collect rainwater, separating blackwater and greywater lines, installing meters, low-water-use appliances and fixtures, and adding underground storage tanks for both rainwater and greywater. This house has achieved a 24% reduction in total water use and a 47% reduction in municipal water use as compared to a typical Tucson residence.49 This project also helped to establish a method for measuring residential water efficiency known as the W-Index. It was shown that while a typical Tucson residence used approximately 148 gpcd, a fully conserving home could use as little as 35 gpcd.50 It is estimated that if 30% of the population implemented a water reuse system in their homes, it would produce a 43% reduction in groundwater overdraft in the Tucson area by the year 2025.51 While all this data collection has been going on, the house has been visited by some 13,000 people, and has received international media coverage.52

The city of Tucson has also been active in the promotion of xeriscaping methods. Each year, a xeriscaping conference is held in the city, as well as a contest awarding the best xeriscaping project. More official tactics have also been used. One regulation prevents the use of municipal groundwater supplies for irrigating areas within public rights-of-way unless the landscaping uses plants from a low-water use list.53 Many other states in the U.S. have enacted such regulations, most notably Texas, which requires xeriscape landscaping of all State buildings and roadside parks.54 Several xeriscape demonstration gardens have also been planted throughout the state; these are open for public viewing.55

Another water conservation project was Watercycle, located at the Millenium Dome in the United Kingdom. This unit was designed to supply up to 500 cubic meters per day of reclaimed water for toilet flushing. 55% of the total water demand for Millenium Dome was met by the Watercycle project. Over 6 million visitors observed this technology in the year 2000, and visitor surveys showed very positive attitudes.56


New integrated water resources management plans involve controlling both water supply and demand. Managing water demand through water conservation and recycling techniques has proven successful. Between 1980 and 1995, the U.S. population grew 16%, but water withdrawal dropped nearly 10%, due largely to increased water demand management.

Despite successful projects, public acceptance of water conservation methods is not at the level some would like it to be. This is largely attributable to limited public awareness of an ongoing problem. Many homeowners are reluctant to alter their water use behavior until a crisis is obvious. Homeowners also perceive restrictions on how they can manage their own homes as personal intrusions.

However, the methods do seem to be gathering approval in drier regions, such as the Southern and Western United States. Efforts to show the benefits of lowering water use are ongoing. It is hoped that one day water users will be able to see and accept the ecological, environmental, economic and personal benefits of implementing these changes.


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