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Type of wastewater generated in households without toilet wastewater

Greywater (or grey water, sullage, also spelled gray water in the United States) refers to domestic wastewater generated in households or office buildings from streams without fecal contamination, i. e., all streams except for the wastewater from toilets. Sources of greywater include sinks, showers, baths, washing machines or dishwashers. As greywater contains fewer pathogens than blackwater, it is generally safer to handle and easier to treat and reuse onsite for toilet flushing, landscape or crop irrigation, and other non potable uses. Greywater may still have some pathogen content from laundering soiled clothing or cleaning the anal area in the shower or bath. The application of greywater reuse in urban water systems provides substantial benefits for both the water supply subsystem, by reducing the demand for fresh clean water, and the wastewater subsystems by reducing the amount of conveyed and treated wastewater. Treated greywater has many uses, such as toilet flushing or irrigation.

Greywater usually contains some traces of human waste and is therefore not free of pathogens. Synthetic personal care products (e. g. toothpaste, face wash, and shower gel) commonly rinsed into greywater may contain microbeads, a form of microplastics. Greywater originating from washing clothes made from synthetic fabrics (e. g. nylon) is also likely to contain microfibers. The small traces of feces that enter the greywater stream via effluent from the shower, sink, or washing machine do not pose practical hazards under normal conditions, as long as the greywater is used correctly (for example, percolated from a dry well or used correctly in farming irrigation).

Global water resource supplies are shrinking. According to a report from the United Nations, water shortages will affect 2.7 billion people by 2025, which means 1 out of every 3 people in the world will be affected by this problem. Reusing greywater has become a good way to solve this problem, and wastewater reuse is also called recycled or reclaimed water.

Greywater use for irrigation appears to be a safe practice. A 2015 epidemiological study found no additional burden of disease among greywater users irrigating arid regions. The safety of reuse of greywater as potable water has also been studied. A few organic micropollutants including benzene were found in greywater in significant concentrations but most pollutants were in very low concentrations. Fecal contamination, peripheral pathogens (e. g., skin and mucous tissue), and food derived pathogens are the three major sources of pathogens in greywater. Greywater reuse in toilet flushing and garden irrigation may produce aerosols. These could transmit legionella disease and bring a potential health risk for people. However, the result of the research shows that the health risk due to reuse of greywater either for garden irrigation or toilet flushing was not significantly higher than the risk associated with using clear water for the same activities.

Most greywater should be assumed to have some blackwater type components, including pathogens. Greywater should be applied below the surface where possible (e. g., via drip line on top of the soil, under mulch; or in mulch filled trenches) and not sprayed, as there is a danger of inhaling the water as an aerosol. In any greywater system, it is important to avoid toxic materials such as bleaches, bath salts, artificial dyes, chlorine based cleansers, strong acids/alkali, solvents, and products containing boron, which is toxic to plants at high levels. Most cleaning agents contain sodium salts, which can cause excessive soil alkalinity, inhibit seed germination, and destroy the structure of soils by dispersing clay. Soils watered with greywater systems can be amended with gypsum (calcium sulfate) to reduce pH. Cleaning products containing ammonia are safe to use, as plants can use it to obtain nitrogen. A 2010 study of greywater irrigation found no major health effects on plants, and suggests sodium buildup is largely dependent on the degree to which greywater migrates vertically through the soil. Some greywater may be applied directly from the sink to the garden or container field, receiving further treatment from soil life and plant roots. The use of non toxic and low sodium soap and personal care products is recommended to protect vegetation when reusing greywater for irrigation purposes.

Devices are currently available that capture heat from residential and industrial greywater through a process called drain water heat recovery, greywater heat recovery, or hot water heat recycling. Rather than flowing directly into a water heating device, incoming cold water flows first through a heat exchanger where it is pre warmed by heat from greywater flowing out from such activities as dish washing or showering. Typical household devices receiving greywater from a shower can recover up to 60% of the heat that would otherwise go to waste.

Government regulation governing domestic greywater use for landscape irrigation (diversion for reuse) is still a developing area and continues to gain wider support as the actual risks and benefits are considered and put into clearer perspective. "Greywater" (by pure legal definition) is considered in some jurisdictions to be "sewage" (all wastewater including greywater and toilet waste), but in the U. S. states that adopt the International Plumbing Code, it can be used for subsurface irrigation and for toilet flushing, and in states that adopt the Uniform Plumbing Code, it can be used in underground disposal fields that are akin to shallow sewage disposal fields. Wyoming allows surface and subsurface irrigation and other non specific use of greywater under a Department of Environmental Quality policy enacted in March 2010. California, Utah, New Mexico and some other states allow true subsurface drip irrigation with greywater. Where greywater is still considered sewage, it is bound by the same regulatory procedures enacted to ensure properly engineered septic tank and effluent disposal systems are installed for long system life and to control spread of disease and pollution. In such regulatory jurisdictions, this has commonly meant domestic greywater diversion for landscape irrigation was either not permitted or was discouraged by expensive and complex sewage system approval requirements. Wider legitimate community greywater diversion for landscape irrigation has subsequently been handicapped and resulted in greywater reuse continuing to still be widely undertaken by householders outside of and in preference to the legal avenues. However, with water conservation becoming a necessity in a growing number of jurisdictions, business, political and community pressure has made regulators seriously reconsider the actual risks against actual benefits. It is now recognized and accepted by an increasing number of regulators that the microbiological risks of greywater reuse at the single dwelling level where inhabitants already had intimate knowledge of that greywater are in reality an insignificant risk, when properly managed without the need for onerous approval processes. This is reflected in the New South Wales Government Department of Water and Energy's newly released greywater diversion rules, and the recent passage of greywater legislation in Montana. In the 2009 Legislative Session, the state of Montana passed a bill expanding greywater use into multi family and commercial buildings. The Department of Environmental Quality has already drafted rules and design guidelines for greywater re use systems in all these applications. Existing staff would review systems proposed for new subdivisions in conjunction with review of all other wastewater system components. Strict permit requirements in Austin, Texas, led to issuance of only one residential graywater permit since 2010. A working group formed to streamline the permitting process, and in 2013, the city created new code that has eased the requirements, resulting in four more permits. In California, a push has been made in recent years to address greywater in connection with the State's greenhouse gas reduction goals (see AB 32). As a large amount of energy (electricity) is used for pumping, treating and transporting potable water within the state, water conservation has been identified as one of several ways California is seeking to reduce greenhouse gas emissions. In July 2009, the California Building Standards Commission (CBSC) approved the addition of Chapter 16A "Non potable Water Reuse Systems" to the 2007 California Plumbing Code. Emergency regulations allowing greywater reuse systems were subsequently filed with the California Secretary of State August 2009 and became effective immediately upon filing. Assembly Bill 371 (Goldberg 2006) and Senate Bill 283 (DeSaulnier 2009) directed the California Department of Water Resources (DWR), in consultation with the State Department of Health Services, to adopt and submit to the CBSC regulations for a State version of Appendix J (renamed Chapter 16 Part 2) of the Uniform Plumbing Code to provide design standards to safely plumb buildings with both potable and recycled water systems. November 2009 the CBSC unanimously voted to approve the California Dual Plumbing Code that establishes statewide standards for potable and recycled water plumbing systems in commercial, retail and office buildings, theaters, auditoriums, condominiums, schools, hotels, apartments, barracks, dormitories, jails, prisons and reformatories. In addition, the California Department of Housing and Community Development has greywater standards and DWR has also proposed dual plumbing design standards. In Arizona, greywater is defined as water with a BOD5 less than 380 mg/L, TSS<430 and the Fats, Oil, and Grease (FOG) content should be less than 75 mg/L. The Arizona water has issued advice that people should avoid direct contact with greywater. Most greywater use is by underground drip irrigation since surface irrigation is not permitted. There are three types of use in Arizona: up to a quota of 400 gpd per family (close to 1500 L per day) no permission is required for greywater use, between 400 and 3000 gpd (1500 and 11,355 L per day, respectively) permission is required and above 3000 gpd (>11,355 L per day) it is considered as conventional wastewater venture. Other limitations include restrictions on contact, restrictions on use on herbaceous food plants, exclusion of hazardous materials and effective separation from surface water run off. The Uniform Plumbing Code, adopted in some U. S. jurisdictions, prohibits gray water use indoors.

Greywater recycling is relatively uncommon in the UK, largely because the financial cost and environmental impact of mains water is very low. Greywater systems should comply with BS8525 and the Water Supply (Water Fittings) Regulations in order to avoid risks to health. Greywater from single sewered premises has the potential to be reused on site for ornamental, garden and lawn irrigation, toilet flushing. The reuse options include Horizontal flow reed bed (HFRB), Vertical flow reed bed (VFRB), Green roof water recycling system (GROW), Membrane bioreactor (MBR) and Membrane chemical reactor (MCR).

Although Canada is a water rich country, the center of the country freezes in the winter and droughts happen some summers. There are locations where watering outdoors is restricted in the dry season, some water must be transported from an outside source, or on site costs are high. At present, the standards for greywater reuse are not strict compared with other countries. Health Canada has published a guideline to use greywater for toilet flushing and British Columbia's building code includes subsurface irrigation with greywater. In Alberta "Reclaimed wastewater from any source cannot be used domestically unless it is approved and meets water quality testing and monitoring by the local municipality." Saskatchewan also treats greywater as sewage.

Household greywater from a single contaminated site may be reused on site at the ornamental garden and lawn watering, toilet flushing and laundry uses, depending on the type of greywater and treatment level. Some people wisely re use the gross weight, but others use it even worse (without any treatment), such as bathing in the bath or simply transferring laundry water to the lawn where children and pets may be exposed directly. The Department of Health and Community Services (DHCS) focuses on protecting public health and then takes action to control and minimize the public health risks associated with greywater reuse.

The government of Cyprus has implemented four water saving subsidies: drilling installations, drilling with lavatories, installation of hot water circulation systems and installation of greywater recycling systems.

The emphasis on the use of greywater in Jordan has two main purposes: water conservation and socioeconomic aspects. The Amman Islamic Water Development and Management Network (INWRDAM) in Jordan promoted research on gray water reuse in Jordan. At present, greywater research in Jordan is funded mainly by the International Development Research Center (IDRC) in Ottawa, Canada, to install and use greywater systems based on the establishment of small wetland systems in private households. The cost of this system is about 500 US dollars per household.