The Benefits and Dangers of Reusing Gray Water

One of the three key principles of green building is "reuse." But how can this principle be applied to the water we use for our homes?

Grey water systems provide an answer, but they must be carefully designed, built and used in order to be effective. In fact, if grey water systems aren't fully understood, an unsuspecting homeowner could do more harm to the environment than good.

Grey water systems, however, have been encouraged by Pacifica's recent  and by using them, we seek to get more use from the water we consume by offering dual benefit for each drop that flows through it. Laundry waste water, sink waste water and shower waste water offer opportunities for reuse by diverting drainage to landscape irrigation.

How they work:

Grey water systems can be simple or complex, depending on the location, budget and preference of each user. Simple systems consist of a container placed below the sink or laundry and a pump or hose delivering the grey water to outside irrigation. Moderate systems are designed to use grey water from multiple sources, capture more water and deliver it to a gravity-fed sub-surface drip irrigation system. More complex systems consist of dual plumbing to deliver water from sinks and laundry for use by toilets as well as landscape irrigation.

How to use them:

It's important to note that grey water systems require the owner to understand the chemistry of the products they use in the first stage of the system. Hand soaps, laundry detergents, and dish soaps must be non-toxic and biodegradable. Otherwise, the downstream uses will be undermined. I've not met anyone yet who wants to use bleaches, surfactants or acids to feed their roses. Furthermore, if someone in your home is suffering from an infectious disease the use of the grey water system must be discontinued. Using a grey water system reminds me of several villages on the banks of a river; the prosperity of the villages downstream relies upon the cleanliness and stewardship of the villages upstream. What you put into the system is what you get out.

What not to do:

• Do not use grey water to grow food crops
• Do not use grey water systems if you have an infectious disease
• Do not pour toxic chemicals into a grey water system
• Do not use grey water indoors except for toilets
• Do not use grey water when laundering diapers or dying clothing
• Do not allow grey water to leave your property

The advantages of grey water reuse:

It's estimated that the average person can save 40 gallons of water daily from the use of a grey water system. In addition, less water used means more fresh groundwater remains available for drinking or growing food. And last but not least, grey water reuse means less water is processed by the local sewage treatment plant and less wastewater is contaminated by human waste.

Grey water systems are not for everyone, but more and more cities like Pacifica are identifying the water conservation opportunities that they represent. The new Green Building Ordinance encourages the use of these systems although, to date, few have been installed. Currently, grey water systems in Pacifica must be reviewed by San Mateo County before they'll issue a permit, but it's comforting to know that the local government is open to their use.