Greywater
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.
The quality of greywater can deteriorate rapidly during storage because it is often warm and contains some nutrients and organic matter (e.g. dead skin cells), as well as pathogens.
[4] Synthetic personal care products (e.g. toothpaste, face wash, and shower gel) commonly rinsed into greywater may contain microbeads, a form of microplastics.
If collected using a separate plumbing system from blackwater, domestic greywater can be recycled directly within the home, garden or company and used either immediately or processed and stored.
Recycled greywater of this kind is never safe to drink, but a number of treatment steps can be used to provide water for washing or flushing toilets.
In times of drought, especially in urban areas, greywater use in irrigation or toilet systems helps to achieve some of the goals of ecologically sustainable development.
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.
[17] 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.
The danger of biological contamination is avoided by using: Greywater recycling without treatment is used in certain dwellings for applications where potable water is not required (e.g., garden and land irrigation, toilet flushing).
Indoor grey water reuse requires an efficient cleaning tank for insoluble waste, as well as a well regulated control mechanism.
"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.
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.
It is now recognized and accepted by an increasing number of regulators[citation needed] 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.
[23] 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.
[25] 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).
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.
Greywater recycling is relatively uncommon in the UK, largely because the financial cost and environmental impact of mains water is very low.
[28] 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).
[32][33] 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.
