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September 5, 2017 > Go green with grey water

Go green with grey water

By Daniel O'Donnell

There are very few things or situations that can be thought of as just black or white; there is usually a grey area. Take a bite from the dark side of a black and white cookie and chocolate will be the prevailing flavor. Take a bite from the white side and it is vanilla. Take a bite down the center where the white and black sides meet and the taste will be a combination of vanilla and chocolate. Water used to be thought of as clean or dirty. Now we know that somewhere in the middle is grey water.

Grey water is shower, sink (non-kitchen), and washing machine water that has been used but can be collected and reused for an additional purpose. Black water is water from a toilet, kitchen sink, or water that contains chemicals, medication, or other pollutants that require the water to be treated before it can be released into the environment. Grey water may have come in contact with humans or animals, natural soaps, or laundry but can be used to water a garden. One of the easiest and most effective ways to reuse grey water is by installing a laundry to landscape or L2L system.

There are a few different ways to get laundry water into a garden. The simplest is by moving the washing machine outside or into the garage and extending the washer's drain hose into the garden. Another elementary system is called the Laundry Drum system. Water can be collected by running the washing machine's drain hose out of a nearby window and into a large drum with a garden hose attached to a spigot at the bottom for immediate use.

A L2L system does not need a permit but will require adherence to some basic rules to ensure safe discharge of the grey water. The two crude systems above make it difficult to follow the requirements, so investing some time and money in a more complex system will be safer and will water the garden more efficiently.

Grey water cannot be stored for future use in any L2L system. It must be diverted to the garden immediately and discharged into a mulch basin. Loads with diapers, dyes, added enzymes, artificial fragrances, and bleach cannot be diverted into the garden. The detergents used have to be biodegradable. Conventional laundry detergents contain salts and chemicals that can kill plants or end up in or on vegetables.

An alternative to biodegradable manufactured detergents would be to use soap nuts or soap berries. Just a couple of these berries from small trees native to warm tropical regions can be placed in the washing machine instead of laundry soap. The organic foamy film from the soap berries is beneficial to many plants. However, the soap nuts must be manually taken out of the washer before the rinse cycle starts so they cannot be used in many front-loading washers because the door locks until the entire cycle is completed. Soap nuts are available on

Installing a more complex L2L system has some mechanical requirements, both near the washing machine and in the garden. The water used will be coming out of the washer's drain hose. Normally the water goes into a sewer pipe, but for a L2L system the drain hose needs to be connected to a three-way valve. This will give the option to send water either into the garden or the sewer by simply turning a lever. One-inch PVC pipe should be used extending from the three-way valve to the sewer drain and the garden. Any smaller diameter pipe will put unnecessary pressure on the washing machine's pump. An air admittance valve will need to be installed at the highest point of the system to prevent back siphoning.

An L2L system is not meant to water an entire garden. It is best suited for watering trees, large shrubs, or planting beds. A top-loading washer can irrigate up to 20 trees or shrubs. A front-loaded washer about 10, and a highly efficient water saving machine about eight. There are mathematical formulas to figure out approximately how much water a plant might need, but they are suited better for irrigation timers where the water availability is consistent. The best way to analyze an L2L system's efficiency is by paying attention to the plant.

Rigid purple PVC pipe should be used in the garden if irrigating in a straight line. Multiple 90-degree elbows can cause friction. Black one-inch flexible line with a purple stripe can be used for more circular patterns and should be labeled for non-human consumption wherever open ends are exposed. Runs should not be longer than fifty feet in flat gardens.

A half-inch line with a flow valve at the end will be used at each irrigation point. The flow valve will allow the water to be reduced at each point down the line so all the water does not go to the first few trees. The last irrigation point should be an open one-inch pipe so water does not back up in the system. It is mandatory for health and safety reasons that at each irrigation point, the grey water drains into a mulch basin. A small box with a purple cover is acceptable for covering each emission point.

Check the system for leaks before burying any lines. L2L supplies and kits can be purchased from Urban Farmer in San Francisco or Richmond ( In a black or white world, grey, as in grey water might be the best compromise.

Daniel O'Donnell is the co-owner and operator of an organic landscape design/build company in Fremont.

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