What are the benefits of using graywater?

• Lower potable water use

• Saves energy used to produce and distribute potable water; along with energy saved from the transport and treatment of wastewater

• Groundwater recharge

• Returns nutrients to the soil

• Effective water treatment occurs in the biologically active upper region of the soil

• Reduces demand on wastewater treatment plants and septic systems

• Allows septic systems to work more efficiently

• Connects homeowners or customers to how much water they are using and their product choices

• Reliable landscape water source during drought or water shortage

• Facilitates local food production;

• Returns vital nutrients to soil.

Whats in Graywater?

If it goes down the drain it ends up in the graywater. Hair, lint, soap, and cleaning products tending to be alkaline(basic).  The water that comes from kitchen sinks is technically considered Blackwater in California (not legally allowed to be reused) though it is more specifically defined as Dark Graywater, and contains food particles, fats and oils that require unique design considerations to be sustainably reused. The high amounts of nutrients and suspended solids and bacteria in graywater rapidly multiply under storage to turn into noxious septic blackwater, which is why graywater is never stored for more than 24 hours. .

How can graywater be reused?

Greywater can be reused for outdoor irrigation through low tech- gravity fed systems, or high tech- systems including filtration, tanks, pumps and drip irrigation. Greywater can also be reused indoors (example: toilet flushing), though requires filtration and disinfectant and currently is not allowed under California code.

Is Graywater hazardous?

There has never been a single documented case of illness from greywater contact or ingestion, though regardless all systems should be designed to avoid the possibility for potential contact with pathogens. Improper designs could create a cross connection where greywater could enter potable water pipes. Potential environmental pollution can result if harmful chemicals in greywater enter the groundwater & surface water. Even naturally occurring nutrients in greywater can contaminate creeks and other surface water by contributing to algae growths that consume oxygen, which is why systems are designed to minimize contact, prevent ponding and runoff and contain graywater onsite.

How do greywater systems work?

There are different designs but most include a collection system to separate graywater from blackwater through what’s referred to as dual-plumbing, a piped distribution system to landscape infiltration areas such as mulch basins or drip-irrigation zones, and a diversion mechanism that allows a way to easily switch the graywater back to a sewer/septic system in case your graywater becomes contaminated (ie. washing hands covered in automotive grease or cleaning toxic paint brushes, etc.) or if seasonally high groundwater levels or precipitation makes it impossible to infiltrate graywater without contamination occurring. The simplest distribution systems are landscape direct, meaning they have no storage or filtration and just passively flow directly into the landscape as the graywater is being produced, while other high-tech systems use a surge tank, pump, filter and/or controller to achieve highly controlled drip irrigation.

When is Graywater produced?

The timing and frequency of graywater production is one of its unique qualities that affect system design.  Graywater production depends upon habitual human behaviors often difficult to control (ie. a whole family of people all showers in the morning, resulting in a huge surge of greywater in a short time), so having sufficient surge capacity in the system is crucial. Graywaters’ albeit consistent production tends to NOT vary according to changing irrigation requirements (people don’t really produce more greywater in a dry summer than they do in a wet winter), so many greywater-irrigated landscapes require a supplementary make-up water system (usually freshwater), which is a chronic source of redundant overwatering in greywatered areas resulting in unrealized water savings.

When NOT to use graywater?

A minimum amount of area is needed to be able to continuously infiltrate the graywater without overflow and runoff occurring (which can cause contamination and is prohibited), and some sites may not have sufficient space to sustainably infiltrate all their graywater. Releasing graywater in close proximity (within 100 ft) to streams, lakes, water wells, or drainage ways may inevitably lead to surface or drinking water contamination and is prohibited. A few sites may have unsuitable soil that is either extremely permeable (potentially contaminating the groundwater) or impermeable (= runoff or ponding). Many buildings that are built on-slab have inaccessible drain pipes that are encased in a concrete slab difficult to modify without substantial demolition.

Should my Graywater system have a pump or not?

There are different advantages and disadvantages to both pumped systems and non-pumped (gravity fed) systems.

Gravity fed systems are: 

• Simple and robust

• Low maintenance

• Relatively inexpensive

• No supplemental electricity

• Some types of systems don’t require permit

• Low water use efficiency (mulch basins)

• Best for trees and shrubs

Pumped Systems
 are:

• Higher water use efficiency

  (if successfully using drip irrigation)

• Able to send water uphill and long distances

• Able to distribute to plants, good for large and small plants

• Increased cost and complexity

• Higher environmental impact from high-tech components