The Greywater Guerrillas
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Greywater Links

Greywater Central, at Oasis Designs. A very comprehensive site.

Introduction to Greywater Management by EcoSanRes.

High-end greywater systems from Clivus Multrum.

California's Graywater Guide Book and code -- mandates very restrictive and expensive systems.

Water CASA- has downloadable publications and explanation of the best state greywater code, Arizona.

The City of Malibu, CA's Graywater Handbook.

Greywater.com

Recycling Water the Greywater Guerrillas' Way

Greywater is water that flows down sink, shower, and washing machine drains--but not the toilet. Greywater may contain traces of dirt, food, grease, hair, and household cleaning products. While greywater may look “dirty,” it is a safe and even beneficial source of irrigation water. If released into rivers, lakes, or estuaries, the nutrients in greywater (mainly phosphate from detergent) become pollutants, but to garden plants, they are valuable fertilizer. Aside from the obvious benefits of saving water (and money on your water bill), reusing your greywater keeps it out of the sewer or septic system, thereby reducing the chance that it will pollute local water bodies Reusing greywater for irrigation reconnects urban residents and our backyard gardens to the natural water cycle. 

The easiest way to use greywater is to pipe it directly outside and use it to water ornamental plants or fruit trees. This avoids the potential risk of transmitting disease-causing microorganisms. Greywater can be used directly on vegetables as long as it doesn't touch edible parts of the plants. In any direct greywater system, it is essential to put nothing toxic down the drain--no bleach, no dye, no bath salts, no cleanser, no shampoo with unpronounceable ingredients, and no products containing boron, which is toxic to plants. It is crucial to use all-natural, biodegradable soaps whose ingredients do not harm plants. In an effort to reduce phosphate pollution of lakes and rivers, many counties have banned phosphate-based detergents. Most powdered detergent, and some liquid detergent, is now sodium based, but sodium can keep seeds from sprouting and destroy the structure of clay soils. Chose phosphate-based liquid soaps in greywater systems. While you're at it, watch out for your own health: "natural" body products often contain substances toxic to humans, including parabens, stearalkonium chloride, phenoxyethanol, polyethelene glycol (PEG), and synthetic fragrances. (to learn more about what’s in your products, go to www.cosmeticdatabase.com and see how they rate for toxicity). Read our recommendations for soaps and products here.

Greywater is more alkaline than rainwater. Plants that normally grow in acidic soils—for example forest and bog plants—do not tolerate greywater well. Non-phosphate detergents raise the salt content of greywater. In areas with regular rainfall, rainwater leaches salts below the root zone of plants, avoiding these problems. In drylands, salts can be diluted by irrigating alternately with greywater and stored rainwater. 


bamboo

Bamboo grown with greywater infiltrated into mulch basins.

Does your greywater need treatment?

The easiest way to use greywater is to pipe directly to the garden and use it to water ornamental plants or fruit trees. Applying greywater directly to the soil surface or just below it minimizes the risk of transmitting any disease-causing microorganisms greywater might contain. The simplest way to infiltrate greywater is by sending it into a mulch basin or a bucket infiltrator in biologically-active topsoil. Plants consume nutrients and soil organisms break down grease and particles. The most difficult and most problematic use of greywater is for watering lawns. To minimize the possibility of human contact with greywater, expensive underground infiltration lines must be installed. We recommend tearing out your lawn and replacing it with a garden!

In most cases, greywater needs no treatment.  Prefabricated greywater systems (i.e. those made by BRAC) use filters and chlorine disinfection to “treat” greywater. Although greywater can contain some fecal indicator bacteria, there has never been a documented case of greywater-linked illness. Like other long-time greywater users, we have found that crop irrigation poses no significant health threat as long as greywater does not contact edible portions of the plants. Chlorinated greywater will kill beneficial soil organisms and poison your plants.

Greywater will clog up your drip lines and MUST be filtered. Manufactured systems (i.e. ReWater) use sand filters that must be back flushed to remove the particles they trap. Since graywater is high in suspended solids, these systems require a lot of maintenance.  In situations that require drip systems, we recommend first treating water in a wetland, then using a sand filter if more treatment is needed. However, wetland treatment will use up a lot of the potential irrigation water, so these complicated and costly systems makes sense only in apartment buildings where large commercial buildings create large graywater flows. For single-family homes, we recommend the low-tech strategies discussed above.

In addition to being beautiful water gardens in and of themselves, constructed wetlands have another important application. At a small urban site with little or no need for irrigation water, a wetland can keep greywater out of the evil sewer by disposing of it via evapotranspiration by wetland plants.  The larger the wetland, the less greywater you’ll get out at the end, especially during hot weather.  Alternatively, send greywater directly to the garden during the growing season, and use a wetland to “dispose” of the greywater when irrigation water is not needed. In cold climates, where the soil freezes during the winter, constructed wetlands can treat greywater year round. Treated greywater can be released into a sump below the frost line during the winter. For more information on wetlands click here.

BASIC GREYWATER SYSTEMS

Each greywater system will be slightly different, depending on your house and site. These are examples of some of the most common systems.
  • Branched drain 
  • Constructed Wetland 

No matter what kind of system you decide on, it’s important to follow these basic greywater guidelines.

  1. Don’t store greywater (more than 24 hours)
  2. Minimize contact with greywater
  3. Infiltrate greywater into the ground, don’t allow it to pool up or run off (knowing the soil percolation rate of your soil and designing mulch basins will help with this)
  4. Keep your system as simple as possible, avoid pumps, avoid filters that need upkeep.
  5. Match your plants irrigation needs with the amount of greywater they’ll receive.

GREYWATER POLICY

Greywater policies differ state to state. The best policy if for the state of Arizona. They have greywater guidelines to educate residents on how to build simple, safe, efficient, greywater irrigation systems. If people follow the guidelines their systems falls under a general permit and is automatically “legal”, that is, the residents don’t have to apply or pay for any permits or inspections.  

California also has a greywater policy but it is very restrictive and usually makes it unfeasible for people to afford installing a permitted system. Because of this the vast majority of systems in California are unpermitted.  

Some states have no greywater policy and don’t give permits at all, while other states give experimental permits for systems on a case-by-case basis.  

To read about greywater policy visit Art Ludwig’s policy page, or read our summary of greywater recommendations.