Q. What is Greywater?

A.  As its name connotes, greywater is of lesser quality than potable water, but of higher quality than black water.  Blackwater is water flushed from toilets.  Also, water from the kitchen sink, garbage disposal and dishwasher usually is considered blackwater because of high concentrations of organic waste.  Water from the bath, shower, washing machine, and bathroom sink are the sources of greywater.

Q.  How can greywater be used?

A. Not a water for all uses, greywater is most suitably used for subsurface irrigation of nonedible landscape plants.  Greywater could supply most, if not all the irrigation needs of a domestic dwelling landscaped with vegetation of a semiarid region.  Along with its application to outside irrigation, graywater can be used in some situations for toilet flushing.

Q.  How much greywater will I have available to use?

A.  The amount of water a household uses for interior and exterior purposes determines to some extent the family's potential greywater supply and demand. A percentage of a household's interior use represents supply, and its exterior applications generally represent demand.

The amount applied to interior and exterior uses greatly varies among different households. For example, interior uses range between 100 percent to 20 percent of the total family water budget. About 60 to 65 percent of water applied to interior uses potentially can be recycled as greywater.

A household applies from zero to 80 percent of its total water budget for exterior uses depending upon a number of variables including type of landscaping, season of the year, residents' water use habits, etc. Greywater can be used to meet many exterior water needs.

Q.  What are the advantages and disadvantages of using greywater?

A.   Not only does its use on landscape conserve potable water, but greywater actually may be better for plants, its use resulting in more vigorous vegetation.  Greywater may contain detergents with nitrogen or phosphorus which are plant nutrients.  It may also contain, however, sodium and chloride which can be harmful to some sensitive species.

Greywater use also offers potential financial advantages to regional sewage treatment facilities. Their capital and operational expenditures may decrease because greywater use diminishes sewer flows, thereby lessening the need to expand such facilities.  Diminished sewer flows from domestic graywater use may have a downside however. Some officials fear this situation will result in insufficient sewer flows to carry waste to the sewer plant.  Others see this as an unlikely problem, except possibly for se wer systems lacking significant slope.

Q.  What are the health hazards with using greywater for irrigation?

A.  Most officials agree that more work and research is needed to determine the risks--and benefits--of greywater use.

Q.  Why is it so difficult to get health department approval to use greywater while so easy to get approval for composting toilets - it seems like it would be the other way around?

A. Health departments and inspectors tend to look for the worst possibility rather than at what you're actually going to do.   Composting toilets, though dealing with much more difficult-to-process material, are a more well-defined system.  Inspectors often feel like they know what you're going to put into a composting toilet but wonder what you will put into your greywater - daring? photographic chemicals? jewelry making acids?

Q. How can I deal with an inspector who doesn't seem open to possibility of using graywater?

A. The first step would be giving him a copy of, "Builder's Greywater Guide". This includes an annotated copy of California's approved greywater regulations. If still unconvinced, find an engineer who will talk to him for you.  This could could cost up to $500 but should get you through the approval process fairly easily.  

Q.What books are available on greywater systems?

A. Washwater Garden, $19.95; Builder's Greywater Guide, $20.95; Create an Oasis with Greywater, $20.95; Branched Drain Greywater Systems, $14.95; The Toilet Papers, $11.00; Low-Cost Sanitation, $31.95; Sustainable Sewage, $21.95, and many more.  Go to our Village Library and Under the "Sanitation, Waste and Greywater" section of the Village Elders' Library, you will find many selections.

Q.How expensive is a greywater system?

A.  Greywater systems vary from simple low-cost systems to highly complex and costly systems. The technology involved in such systems ranges from the sophisticated to the crude, from engineered systems with filters and pumps to a washing machine draining directly onto oleander bushes. (Official acceptance correspondingly varies from approval to disapproval.)

Greywater recycling systems are commercially available.  The more sophisticated greywater systems treat greywater prior to disposal to reduce groundwater contamination and surface ponding problems.  Some of these systems are able to remove pollutants and bacteria from graywater.  The better systems include settling tanks and sand filters.  Improvement in technologies and systems' innovations regularly occur.

Expensive units are indeed available, but a person interested in greywater use is not limited to these options.  With a modicum of mechanical skills, a person can devise or improvise methods to use greywater.  In fact, these activities invite the ingenuity of backyard technology.

For example, a greywater use system was designed to recycle washing machine rinse water back into the washer for use in the wash cycle of the next load.  Clothes thus are washed in the rinse water from the previous load, and water is saved.  This system consists of a 32-gallon trash container placed adjacent to a washing machine, but at a slight elevation.  After the wash cycle has drained, the drain hose from the washing machine is removed from the sewer standpipe and positioned to drain the rinse water into the container.  The rinse water later flows back into the washing machine through a one-inch gate valve for use in the wash cycle of the next load.

Q.  Can you use a pump?

A.  Yes.  The sump fills to a level that activates a float switch and then the graywater can be pumped into various treatment systems.  The greywater then is pumped through an underground drip irrigation system to the landscape or for use in the toilet.

Common greywater mistakes from the Book Create an Oasis with Greywater, item #VE12219

This page was updated in February 2008.  We will be adding additional FAQs soon!

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