Giving Water Two Lives

This garden is watered by wastewater, or "graywater," from a washing machine.

With the departure of winter rains, most of us have had to turn on the sprinklers by now to help plants thrive in our hot, dry summers. However, we can minimize water use in the landscape with practices such as choosing low-water use plants, applying mulch, and efficient irrigation practices. You can also reuse household water, or “graywater,” in the landscape, which is a great way to get more bang for your buck.

Graywater can be summed up as everything but the kitchen sink (and the toilet); wastewater from showers, bathroom wash basins, and washing machines can all be used. Water from kitchen sinks and dishwashers have high levels of organic matter, and a correspondingly higher potential for pathogens so are not permitted as graywater sources without treatment before reuse.

Although redirecting wastewater from bathtubs and sinks requires a permit, homeowners can install a system connecting their washing machine to the garden without a permit. Also known as laundry-to-landscape, there are 13 do’s and don’ts mandated by Chapter 15 of the California Plumbing Code. They won’t all be listed here, but they boil down to minimizing contamination. A full list of California’s codes and policies for graywater can be viewed at greywateraction.org.

The specific layout of your system will vary, depending on the set-up of your washing machine and landscape. All systems are required to have a diversion with a three-way valve, which sends the wastewater either out to the garden or to the sewer/septic system. This allows you to keep water that may contain certain chemicals or biohazards (e.g. diaper wash water) from entering your landscape. Once the diversion pipe exits the house, it is sent to a mulch basin which consists of an outlet chamber in which mulch replaces the top several inches of soil. There needs to be air space between the drain outlet and the mulch surface so that roots do not grow back into the pipe. Details and other considerations for laundry-to-landscape systems can be found at oasisdesign.net/greywater/laundry.

When deciding if you want to install a graywater system, consider what you will be irrigating. Fruit trees are great because they require regular watering. In a hot climate such as ours, a medium-sized fruit tree can use 30-50 gallons of water a week. Ornamental shrubs and trees with moderate to high water requirements are also great, but low-water use plants will not like being watered several times a week. It is possible to water lawns with graywater via subsurface drip irrigation, but installation can be expensive and you need to generate a lot of graywater in order to break even. It’s better to grow fruit trees and turn that used water into food!

To irrigate trees, a branched drain system can be added. This will disperse water from the outlet chamber to a mulch basin surrounding the tree. If you have an established tree, it is best to dig a basin around the drip line (the outer edge of the canopy), which is where the plant’s feeder roots are. Roots closer to the trunk are larger, and cutting into them causes more damage. For heavier soils, make sure the the tree is elevated above the basin so that water does not collect around the crown, creating the potential for rot.

If you are only running a couple loads of laundry a week with an efficient front-load machine, then this system may not be worth the effort. If you find that you do not produce much wastewater (which is great) but still want to use a laundry-to-landscape system, direct the water to shallow-rooted plants. If you put small amounts of water around a deep-rooted tree, it won’t benefit much. Some plants are more sensitive to salts than others and could be damaged with the constant application of graywater. Azaleas and strawberries are two examples of salt-sensitive plants.

An important rule of thumb for graywater systems is that what goes in must come out. Certain chemicals in laundry products can be harmful to plants, especially if applied over the long term. Chlorine is often added to bleach, which can cause new foliage to look bleached. Boron is sometimes added to detergents under the name borax, but also damages foliage by causing leaf edges to look burnt. If you need to use products that could potentially harm your plants, use that three-way valve to send the wastewater out to the sewer instead. A list of landscape-safe cleaning products can be found at ecologycenter.org/factsheets.

If you have a gardening related question you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website: sjmastergardeners.ucanr.edu.

This entry was posted in Uncategorized. Bookmark the permalink. Post a comment

Post a Comment

You must be logged in to post a comment.

We reserve the right to remove any content at any time from this Community, including without limitation if it violates the Community Rules. We ask that you report content that you in good faith believe violates the above rules by clicking the Flag link next to the offending comment or fill out this form.
  • Blog Author

    Nadia Zane

    Nadia Zane is a UC Master Gardener, a landscape designer and Stockton native. She has a fondness for California native plants and sustainable landscaping, which she utilizes in her work for Native Beauty Garden Design. She is a member of the CA ... Read Full
  • Categories

  • Archives