Greywater is water from sinks, showers and washing machines. It is NOT water from toilets (that's called blackwater). Approximately 80% of household water is greywater and reusing some of this in your yard can be a safe and easy way to save water and money.
Greywater reuse can reduce most households' water bill by 10 to over 50%. Click here for our one page handout on greywater
Ways to reuse greywater
1. OUTDOOR IRRIGATION USE: LANDSCAPE DIRECT
Simple greywater systems send greywater directly to the landscape. They use gravity when ever possible, and are designed not to need filters. Such systems can cost from a couple of hundred to a few thousand dollars, and are the type typcially installed by us at residential sites.
2. OUTDOOR IRRIGATION USE: DRIP IRRIGATION
More complicated greywater systems use filters to treat greywater before sending the water to a drip irrigation system; all particles must be removed to avoid clogging the drip irrigation systems, and filters must be automatically cleaned so forgetful behavior doesn't ruin the entire system! Such systems can cost $5,000 and $10,000.
3. INDOOR GREYWATER USE- TOILET FLUSHING
Complex greywater systems filter and disinfect greywater before using it to flush toilets. Such systems are expensive to build and maintain, so are most appropriate for multi-family and commerical buildings.
Basic Guidelines for landscape direct systems
Greywater is different from fresh water and thus requires different guidelines for it to be reused.
1. Do not store greywater for longer than 24 hours. As nutrients in greywater breakdown, they can create bad odors.
2. Minimize contact with greywater. Greywater, like the soil in most yards, could be potentially dangerous if ingested, so it should not be exposed where children or animals could drink it.
3. Infiltrate greywater into the ground. If greywater pools or runs off the site it can created breeding grounds for mosquitos and increases the risk that a human or animal come in contact with it.
4. Avoid pumps and filters that need to be maintained. Simple systems last longer, require less maintenance, consume little or no energy and cost less.
5. Install a 3-way valve to allow for switching between the greywater system and the sewer or septic system.
6. Match production with demand. The greywater system needs to balance the amount of greywater a household generates with the needs of the plants and trees in the landscape.
Washing machines are typically the easiest source for greywater because the greywater can be diverted without cutting into the existing plumbing. The machines internal pump can pump greywater directly to the plants.
Showers can produce large quantities of greywater containing few solids and dilute soaps. Accessing the shower greywater requires cutting into the drain line. A simple gravity-based greywater system can be designed if the garden is downhill of the shower. If the garden is uphill from the house a pumped system will be required.
Legal aspects of greywater
In the US, greywater codes vary from state to state. The codes in Arizona, Texas, and New Mexico make it easy for people to reuse greywater legally. California revised its code in August of 2009 so it is easy and legal to instal some types of greywater systems.
Greywater Resources
Greywater Action (www.greywateraction.org) Oasis Design (www.oasisdesign.net)
