How to create your own Grey water system

Grey water is gently used 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.

Grey water may contain traces of dirt, food, grease, hair, and certain household cleaning products. While grey water may look “dirty,” it is a safe and even beneficial source of irrigation water in a yard. Keep in mind that if grey water is released into rivers, lakes, or estuaries, its nutrients 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 grey water 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 grey water is to pipe it directly outside and use it to water ornamental plants or fruit trees. Grey water can also be used to irrigate vegetable plants as long as it doesn’t touch edible parts of the plants.

In any grey water system, it is essential to use “plant friendly” products, those without salts, boron, or chlorine bleach. The build-up of salts and boron in the soil can damage plants. Look for products and soaps that DON’T include Sodium Lauryl sulphates.

I believe that for residential grey water systems simple designs are best. With simple systems you are not able to send grey water into an existing drip irrigation system, but must shape your landscape to allow water to infiltrate into the soil. I recommend simple, low-tech systems that use gravity when ever possible, instead of pumps. I prefer irrigation systems that are designed to avoid clogging, rather than relying on filters and drip irrigation.

I promote grey water 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–grey water, 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.

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.

Basic Grey water Guidelines

Grey water is different from fresh water and requires different guidelines for it to be reused.

Don’t store grey water (more than 24 hours). If you store grey water the nutrients in it will start to break down, creating bad odors.

Minimize contact with grey water. Grey water 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.

Infiltrate grey water 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 grey water can provide mosquito breeding grounds, as well as a place for human contact with grey water.

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.

Install a 3-way valve for easy switching between the grey water system and the sewer/septic.

Match the amount of grey water your plants will receive with their irrigation needs.

Types of Simple Systems

From the Washing Machine

Washing machines are typically the easiest source of grey water to reuse because grey water 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 grey water directly to your plants.

Laundry-to-Landscape

If you’re looking for 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 invented by Art Ludwig.

This grey water system doesn’t alter the household plumbing: the washing machine drain hose is attached directly to a diverter valve that allows you to switch the flow of grey water between the sewer/septic and the grey water irrigation system. The grey water irrigation system directs water through 1″ tubing with 1/2″ outlets directing 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 grey water system!

From the Shower

Showers are a great source of grey water- they usually produce a lot of relatively clean water. To have a simple, effective shower system consider a gravity-based system (no pump). If your garden is located uphill from the house, then you’ll need to have a pumped system.

Branched Drain

Plants and Grey water system was also invented by Art Ludwig. Grey water 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.

From the Sinks

Kitchen sinks are the source of a fair amount of water, usually very high in organic matter (food, grease, etc.). This water will clog many kinds of systems. To avoid clogging, I recommend using a branched drain system with mulch basins, organic matter collects in the woodchips and decomposes. Since bathroom sinks don’t typically generate much water, they can often combine flows with the shower water. Or, the sink water can be drained to a single large plant, or divided to irrigate two or three plants.

Plants and Greywater

Low tech, simple 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) Bananas, avocados, blueberry trees are best.

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