Greywater is water from your bathroom sinks, showers, tubs, and washing machines. It is not water that has come into contact with feces, either from the toilet or from washing diapers.
Greywater may contain traces of dirt, food, grease, hair, and certain household cleaning products. While greywater may look “dirty,” it is a safe and even beneficial source of irrigation water in a yard. If released into rivers, lakes, or estuaries, the nutrients in greywater become pollutants, but to 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. Greywater can be used directly on vegetables as long as it doesn't touch edible parts of the plants. In any 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. Most powdered detergent, and some liquid detergent, is sodium based, but sodium can keep seeds from sprouting and destroy the structure of clay soils. Chose salt-free liquid soaps. 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 the Cosmetic Database and see how they rate for toxicity). Read our recommendations for soaps and products here.
We believe that for residential greywater systems simple designs are best. With simple systems you are not able to send greywater into an existing drip irrigation system, but must shape your landscape to allow water to infiltrate into the soil. We recommend simple, low-tech systems that use gravity when ever possible, instead of pumps. We prefer irrigation systems that are designed to avoid clogging, rather than relying on filters and drip irrigation.
We promote greywater reuse as a way to increase the productivity of sustainable backyard ecosystems that produce food, clean water, and shelter wildlife. Such systems recover valuable "waste" products--greywater, household compost, and humanure--and reconnect their human inhabitants to ecological cycles. By modeling "appropriate technologies" for food production, water, and sanitation in the industrialized world, we hope to replace the cultural misconception of "wastewater" with the possibility of a life-generating water culture.
We believe more complex systems are best suited for multi-family, commercial, and industrial scale systems. These systems can treat and reuse large volumes of water, and play a role in water conservation in dense urban housing developments, food processing and manufacturing facilities, schools, universities, and public buildings. Because complex systems rely on pumps and filtration systems, they are often designed by an engineer, are expensive to install and may require regular maintenance. If you are interested in learning more about more complicated residential or commercial systems please visit Wahaso or ReWater.
Basic Greywater Guidelines
Greywater is different from fresh water and requires different guidelines for it to be reused.
1. Don’t store greywater (more than 24 hours). If you store greywater the nutrients in it will start to break down, creating bad odors.
2. Minimize contact with greywater. Greywater could potentially contain a pathogen if an infected person's feces got into the water, so your system should be designed for the water to soak into the ground and not be available for people or animals to drink.
3. Infiltrate greywater into the ground, don’t allow it to pool up or run off (knowing how well water drains into your soil (or the soil percolation rate of your soil) will help with proper design. Pooling greywater can provide mosquito breeding grounds, as well as a place for human contact with greywater.
4. Keep your system as simple as possible, avoid pumps, avoid filters that need upkeep. Simple systems last longer, require less maintenance, require less energy and cost less money.
5. Install a 3-way valve for easy switching between the greywater system and the sewer/septic.
6. Match the amount of greywater your plants will receive with their irrigation needs.
Types of simple systems
From the Washing Machine
Washing machines are typically the easiest source of greywater to reuse because greywater can be diverted without cutting into existing plumbing. Each machine has an internal pump that automatically pumps out the water- you can use that to your advantage to pump the greywater directly to your plants.
If you don't want to invest much money the system (maybe you are a renter), or have a lot of hardscape (concrete/patio) between your house and the area to irrigate, we recommend a laundry drum system.
Wash water is pumped into a "drum," a large barrel or temporary storage called a surge tank. At the bottom of the drum the water drains out into a hose that is moved around the yard to irrigate. This is the cheapest and easiest system to install, but requires constant moving of the hose for it to be effective at irrigating.
See an example of a laundry drum system.
If you're looking for a system that gives you flexibility in what plants you're able irrigate and takes very little maintenance, we recommend the laundry to landscape system. This system was first invented by Art Ludwig.
In this system the hose leaving the washing machine is attached to a valve that allows for easy switching between the greywater system and the sewer. The greywater goes to 1" irrigation line with outlets sending water to specific plants. This system is low cost, easy to install, and gives huge flexibility for irrigation. In most situations this is the number one place to start when choosing a greywater system!
From the Shower:
Showers are a great source of greywater- they usually produce a lot of relatively clean water. To have a simple, effective shower system you will want a gravity-based system (no pump). If your yard is located uphill from the house, then you'll need to have a pumped system.
Greywater in this system flows through standard (1 1/2" size) drainage pipe, by gravity, always sloping downward at 2% slope, or 1/4 inch drop for every foot traveled horizontally, and the water is divided up into smaller and smaller quantities using a plumbing fitting that splits the flow. The final outlet of each branch flows into a mulched basin, usually to irrigate the root zone of trees or other large perennials. Branched drain systems are time consuming to install, but once finished require very little maintenance and work well for the long term. Art Ludwig also invented this system.
From the Sinks:
Kitchen sinks are the source of a fair amount of water, usually very high in organic matter (food, grease, etc.). Kitchen sinks are not allowed under many greywater codes, but are allowed in some states, like Montana. This water will clog many kinds of systems. To avoid clogging, we recommend branched drains to large mulch basins. Much less water passes through bathroom sinks. If combined with the shower water it will fall under the shower system, if used alone, it can be drained to a single large plant, or have the flow split to irrigate two or three plants.
See an example of a kitchen sink system here.
If you produce more greywater than you need for irrigation, a constructed wetland can be incorporated into your system to "ecologically dispose" of some of the greywater. Wetlands absorb nutrients and filter particles from greywater, enabling it to be stored or sent through a properly designed drip irrigation system (a sand filter and pump will also be needed- this costs more money). Greywater is also a good source of irrigation for beautiful, water loving wetland plants. If you live near a natural waterway, a wetland can protect the creek from nutrient pollution that untreated greywater would provide. If you live in an arid climate, or are trying to reduce your fresh water use, we don't recommend incorporating wetlands into greywater systems as they use up a lot of the water which could otherwise be used for irrigation.
If you can't use gravity to transport the greywater (your yard is sloped uphill, or it's flat and the plants are far away) you will need a "drum with effluent pump" system. The water flows into a large (usually 50 gallon) plastic drum that is either buried or located at ground level. In the drum a pump pushes the water out through irrigation lines (no emitters) to the landscape. Pumps add cost, use electricity, and will break, so avoid this if you can.
Indoor Greywater use
In most residential situations it is much simpler and more economical to utilize greywater outside, and not create a system that treats the water for indoor use. The exceptions are in houses that have high water use and minimal outdoor irrigation, and for larger buildings like apartments.
There are also very simple ways to reuse greywater inside that are not a "greywater system". Buckets can catch greywater and clear water, the water wasted while warming up a shower. These buckets can be used to "bucket flush" a toilet, or carried outside. There are also simple designs like Sink Positive, and more complicated systems like the Brac system. Earthships have an interesting system that reuse greywater inside with greenhouse wetlands.
Plants and Greywater
Low tech, simple greywater systems are best suited to specific, large plants. Use them to water trees, bushes, berry patches, shrubs, and large annuals. It's much more difficult to water lots of small plants that are spread out over a large area. (like a lawn or flower bed) Read more about recommended plants to water on our plant page.
Greywater policies differ state to state. The best policy is from 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 had the first greywater code in the nation, but it had been very restrictive and usually made it unfeasible for people to afford installing a permitted system. Because of this the vast majority of systems in California are unpermitted. Using data from a study done by the soap industry, Art Ludwig estimates that for every permit given in the past 20 years, there were 8,000 unpermitted systems built. In 2009 California changed it's code, making it much easier for people to build simple, low cost systems legally. The current greywater code in California (2013 CPC) is Chapter 16 of the state plumbing code, download it here. (Note that the much-improved code of 2009 was called Chapter 16A. Now the greywater code is Chapter 16, and Chapter 16A covers recycled water, not greywater.)
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.