15. Landscape Sustainability - Wastewater Reuse
There are many things having to do with water in the landscape that can be better designed for sustainability, such as rainwater harvesting and stormwater. Any garden needs water to thrive, especially if you are growing your own food, but drinkable water is a precious resource that is best saved for quenching your own thirst. We use a lot of water in our homes for washing and cleaning that really doesn’t get that dirty, so why not use it to water the yard?
Wastewater on My Plants?
Yes, actually you can put wastewater to use: I have read that it is possible to use 15-40% less drinking water by diverting some of the dirty water that normally goes down the drain. Household wastewater is divided into two types: grey and black water. Greywater is generally defined as any wastewater except what is flushed down your toilet. The official definition given by State of California is a little different, including only waste water from laundry washing machines, bathroom sinks and showers/bathtubs. The State doesn’t like to include kitchen sinks or dishwashers because of the potential hazards to human health from bacteria and other organisms. However, the water from your washing machine or shower is relatively clean and has potential for reuse. Inside the home, greywater can be reused for flushing toilets, but I want to focus on landscape uses, namely irrigation.
Government Regulation
Greywater systems have been used for a long time in more rustic settings, and pioneered by Californians for modern dwellings since the 1970’s, with little government oversight. My favorite is the ‘garden shower’ where you surround an outdoor shower with dense, water loving plants and the drain connects directly to a distribution system to water them – but you obviously need a lot of land area and privacy to do that! In 2009 the State of California revised their laws regulating the uses of greywater to allow certain types of installations. The legal details are too long to list here, and are still being tinkered with by our lawmakers. But generally a greywater system that only uses water from the washing machine is very lightly regulated, and a system using bathroom sink, shower or bathtub water is allowable with the proper permits.
Laundry to Landscape System
This leads us to the simplest and cheapest option for home greywater use, the laundry to landscape system. This involves a diversion of the water from your laundry’s waste pipe to a low-tech distribution system using mulch basins. It generally does not require a permit, but varies by City and County, so you should confirm it before starting.
A washing machine can generate an average of 15 gallons of water per day, per person, and you can route all of that into the landscape - no small amount! If you’re already on track with a sustainable landscape of native and drought tolerant plants, you can still route this greywater to a special area of higher water use plants, especially fruit trees or non-tuberous vegetables. Greywater should not come into contact with anything you directly touch or eat, so don't use it to irrigate tuberous root crops like potatoes, carrots, etc.
1. Diverting the Water
The first part of the system is a bit of plumbing to divert the water from going into your sewer lines. This involves a T connection with a valve so that you can direct the water outside when you want, and a vacuum breaker. Details on all of the pieces needed can be found in the resources listed below, but generally it is a relatively simple do-it-yourself project. The reason for the valve is so that you always have the option of putting that water into the sewer pipe. This could be necessary if you happened to need to use chlorine bleach on a certain load, or if the soil is already extremely saturated and the greywater will be forced to run across the surface (not legally allowed).
2. Dissipate the water into the landscape
The second part of the system is piping and mulch basins to distribute the water into the soil. In this low-tech system we are avoiding a connection to a typical drip irrigation system so that we don’t have to worry about micro-filtration to prevent clogs in the tiny holes of drip emitters.
The interesting part to me is the mulch basins. The greywater should not come into direct contact with people or animals, so the idea is to have the outlet of the piping below ground in a mulch filled depression that allows temporary pooling up and rapid soaking into the soil. The best low-tech detail I’ve seen is to cut off the bottom of a black nursery pot and use it as a ‘shield’ for the outlet pipe. You want to keep the outlet pipe about 4” above the mulch, but below the ground level, so the pot creates a chamber for this. This is critical because it prevents the pipe from getting clogged up; if all of your outlet pipes became clogged the water won’t have anywhere to go and you’ll break the washing machine. Layout, size and number of mulch basins is determined by some calculations on the amount of water you will have and what area it will serve, described in the resources listed below. There are many other technical details that I’m not able to describe in this short piece, so be sure to read up on it or hire a professional to help you with the design and installation.
New Water Use Habits
Once you have a laundry to landscape system installed, there are a few easy changes to make to your water use habits. The main one is using cleaners that are safe for the garden, avoiding things like chlorine, boron/borax, and high salt content. In the Bay Area we are fortunate to have retail stores that sell biodegradable laundry detergents specifically for greywater systems, they can also be mail ordered. You might also consider changing your laundry schedule, spreading it throughout the week so that the plants are watered on a regular basis. You should also keep up with periodic maintenance of the system, monitoring for clogs, and replacing the mulch in the basins annually.
Hopefully you will find that the knowledge of where this water is going makes you more conscious of your water use in general. As with rainwater harvesting, a greywater system is a practical sustainability feature that also mentally connects you to the ecological systems that you are a part of, an important larger goal of sustainable design.
References:
I’ve really only put a few ripples in the surface of this topic, there are tons of different systems and lots of groups providing free information on them, check out these references for all the details:
San Francisco Greywater Manual for Outdoor Irrigation, sponsored by the SFPUC, downloadable at http://sfwater.org/index.aspx?page=100
Create and Oasis with Greywater, Oasis Design, www.oasisdesign.net
Greywater Action, www.greywateraction.org
Water Management, Occidental Arts and Ecology Center workshop led by Brock Dolman, fall 2012
State of California Greywater Code - NOTE: as of May 2019 this code seems to have been changed or invalidated by a lawsuit, see this link for more information https://www.hcd.ca.gov/building-standards/buiding-code/index.shtml