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Frequently asked questions


What is greywater?

Greywater is a term used to describe wastewater from household uses including laundry, showers, dishwashers and bathroom sinks.  It differs from "blackwater" or sewage in that is does not contain any human waste.  Because of the low amount of contaminants, greywater can be easily recycled for use on-site.  It can be used to irrigate landscapes, create constructed wetlands or ponds, or plumbed indoors to flush toilets.  Using your recycled greywater to flush toilets is a big water-saver, since about 50% of indoor water use is toilet flushing!

Pursuant to Health and Safety Code Section 17922.12, "graywater" means untreated wastewater that has not been contaminated by any toilet discharge, has not been affected by infectious, contaminated, or unhealthy bodily wastes, and does not present a threat from contamination by unhealthful processing, manufacturing, or operating wastes. "Graywater" includes but is not limited to wastewater from bathtubs, showers, bathroom washbasins, clothes washing machines, and laundry tubs, but does not include wastewater from kitchen sinks or dishwashers.



Do greywater systems require a permit?

Permitting requirements for greywater systems will vary according to where you live.  According to Appendix G of the California Uniform Plumbing Code, you do not need a permit for a simple, gravity flow, single-fixture greywater system. This includes a basic Laundry-to-Landscape System! If you are collecting more than one source of greywater, and/or need a pump to deliver pressurized irrigation, you are required to obtain a permit.

Laundry-to-landscape systems, which divert graywater from the washing machine to your garden without cutting into existing plumbing, do not require a permit as long as no pump (other than the washing machine itself) or surge tank is used, and as long as all code requirements are met.

While local codes may vary, here is a sample template from the City of Berkeley's Energy and Sustainable Development website:

System TypePlumbing PermitElectrical PermitBuilding PermitZoning Requirements
Clothes Washer SystemNo*NoNoNone
Simple (<250 gallons)YesYes, if pumpNo**Check with Zoning
Complex (>250 gallons)YesYes, if pumpNo**Check with Zoning


DIG Coop can help you determine the type of permit, if any, that will be required for the kind of system you desire.  DIG will inform you of requirements and will acquire the proper permits before beginning work.  If you are remodeling, we encourage you to plumb your new fixtures to drain to a "greywater stub-out" so you will always have the option of adding a greywater system in the future.

For more information on your locality or permitting requirements generally, visit:

City of Berkeley

Greywater Alliance  

California Uniform Plumbing Code Greywater Chapter 16A  

East Bay Municipal Utility District (EBMUD)

Greywater Action



Can I eat food from my greywater garden?

Greywater should not be used to irrigate root crops or edible parts of food crops that touch the soil.  Always apply greywater directly to the soil, not to an above-ground sprinker that may spray plants.  It is best to use greywater to irrigate established plants rather than young seedlings.  

There are many vegetables that can be trained off the ground or that fruit above ground which can be harvested from greywater-irrgated gardens. This includes hundreds of herbs, medicinal plants and fruits  that grow on shrubs and trees.  



How much water could I save by harvesting rainwater?

While several factors affect the exact amount of rainwater that can be harvested at your site, the quantity can be estimated using a simple rule of thumb. From each square foot of the foot print of the building, about .642 gallons of water will land on the roof per inch of rain. (Of that, about 15% will be lost to wind, deflection and evaporation.) Use the simple formula of 1/2 gallon per square foot of roof area for each inch of rain to estimate your water capture. For example, a 2,000 square foot roof will collect about 1,000 gallons of water per 1-inch rain event, while a 250,000 square foot roof will collect over 125,000 gallons of water.  To get an idea of how much water is used residentially, each person uses approximately 80-100 gallons per day.  That means a family of four would use about 10,800 gallons of water per month!

DIG will help you figure out the best-suited rainwater harvesting system for your site to maximize your savings!


What design principles does DIG use when designing a system?

DIG Coop uses Permaculture principles in designing landscapes and waterwise ecosystems.  

The Permaculture design principles are a set of universal design principles that can be applied to anything that is designed.  However, it was developed primarily for the use of designing productive landscapes that thrive without much human energy input.   They allow us to design beautiful, sustainable human habitats and and food production systems.

Permaculture is a design system that encompasses a wide variety of disciplines, such as ecology, landscape design, environmental science and energy conservation, and the Permaculture design principles are drawn from these various disciplines.  The prinicples are derived from observation of nature, and are based on the way that ecosystems naturally thrive.  

Each individual design principle embodies a complete conceptual framework based on sound scientific principles. When we bring all these separate principles together, we can create a design system that both looks at whole systems, the parts that these systems consist of, and how those parts interact with each other to create a complex, dynamic, living system.

Each design principle is a tool that allows us to integrate all the parts of a design, known as elements, into an integrated system where the elements harmoniously interact and work together in the most efficient way possible.

To learn more about Permaculture in the Bay Area, visit The Urban Permaculture Institute.