Some basic graywater system benefits include groundwater recharge, reduced water usage, reduced discharge into wastewater treatment plants, and increased awareness of the value of water resources. But how does graywater connect to climate change?

Climate change will exacerbate “heat islands” in cities where dark asphalt concentrates heat. The benefits of graywater go a long way in mitigating the heat island effect and generally contribute to a more resilient, thriving community by providing irrigation and nutrient to our tree canopy.

Bigger trees, grown faster

Graywater properly installed grows bigger trees and promotes faster growth. Bigger, greener trees sequester more carbon than stunted, water-deprived ones with curled up, brown leaves. Trees that might not receive any water in the summer months can benefit from graywater as long as showers and laundry are supplying the system.

If fruit or nut trees are a gardener’s choice, inadequate water in the root zone often means poor fruit production. It can also mean more plant pathologies and insect predation. Graywater fed fruit trees mean increased yields and more food for humans.

There are huge projects worldwide planting trees to sequester carbon. Ethiopia was recently in the news planting millions of trees nationwide. There’s no reason we can’t leverage this strategy in our own yards. In fact, the City of Davis and Tree Davis recently received funds to plant 1,000 new trees in our community (see information and links at the end of this article). Real estate agents could tout the added value of large shade trees increasing property values. Win-win situations. No additional potable city water needed to achieve this noble goal.

This apricot tree increased yield dramatically after a graywater system was installed. Photo credit Christine Backman.


Better shading saves on AC costs

Large, verdant tree canopies over roofs insulate in a way that allows air conditioners (ACs) to work less. ACs are such a big part of electricity consumption and carbon contamination, and usage will only increase as predicted heat records continue to be broken. Recently, in Paris, where homes typically do not have air conditioners, a new record was set at 108.3° F! In California new roofs must have foil lined plywood sheeting to keep heat from penetrating into interior spaces. Large trees, greywater fed, work in conjunction with this requirement.

Benefit to bees

If graywater were redirected to flowering trees throughout our community, it would result in better flowering and better overall bee colony health. Graywater irrigation increases nectar-producing capacity and prolongs the duration of nectar supply in plants, both of which decrease in hot weather as root zone moisture decreases and plant stress occurs. It takes seven pounds of nectar to produce a pound of honey, so thousands of bee trips to flowers are required. Naturally, if bees sip more nectar from each flower, they can produce more honey and quicker.

Bees will travel as far as five miles to find nectar sources during local scarcity. When bees can find local nectar sources and don’t have to travel so far, there are obvious benefits. Colony collapse is attributed to various stress factors including varroa mites, ant intrusions, and pesticides. Local bees are not immune to these maladies but do benefit from longer nectar harvesting seasons and local sources.

Don’t forget renters

Young renters need exposure to graywater as one solution to the climate change problem. It can’t just be a white, affluent privileged group that benefits from graywater systems. This is my point: More property owners need to make a concerted effort to install graywater systems at their rental properties. Landlords could provide Oasis laundry soap to be used exclusively by tenants. Fifteen years ago, I installed a simple valve diversion to my front yard drip system to allow the first gallons of cold water to benefit plants. Now a device can be purchased and installed on the shower head that does the diversion automatically. Imagine this system coupled with graywater from the drain heading to your garden.

Graywater can also fill in gaps in communication between renters and property owners when a sprinkler timer fails or renters shut off the sprinklers to save water. Simple gravity-fed systems are low tech and can act independently from timer-controlled sprinklers.

Prolific artichoke blossoms fed by graywater system. Previous year yielded only a few. Photo credit Leslie Crenna.

Free 3-way valves and used materials

I salvage 3-way values from dumped old hot tubs/spas. Used parts incentivize graywater installations because it lowers the cost. Neither laundry nor shower drain systems are high pressure so the need for new components isn’t critical. Recology and UC Davis Recycling could collect valves and the rolls of plastic irrigation hose that often end up in recycling bins in both new and used condition.

Kitchen sink graywater, balancing health concerns, and resource utilization

The issue of using kitchen sink graywater is widely addressed by homeowners and at graywater conferences I have attended. The California legislature has prohibited this alternate water source for health reasons mainly for alleged soil contamination issues. There is no reason to under utilize this valuable resource. The beneficial aspect of kitchen sink water will eventually have to be acknowledged by the legislators.

Some solutions to move graywater forward: City resources and new code

Advocates and the City building department could collaborate on a pamphlet that explains that retrofitting existing construction for graywater is much more difficult than during new construction. Our City should develop guidance for shower graywater systems and add information about the benefits of installing greywater systems as part of new construction or remodels to existing laundry to landscape information. This way homeowners or contractors pulling permits will be apprised of how much easier it is to install systems up front. A new code that requires new construction be plumbed with stub outs for potential future graywater systems is a long-discussed proposal in our community and should move forward.

Visit the Tree Davis Community Canopy request web page to request a free tree

Tree Davis Community Canopy web page

All trees will be planted in the front yard of the property, in accordance with the city’s tree ordinance. The recipient is responsible for watering and care of the tree. Pruning or removal is the city’s responsibility.

Laundry to landscape graywater system as it collects discharge from a washer in Davis. Photo credit Johan Verink.

More Information

Greener Davis Newsletter

Paris Hits Sweltering New Heat Record, Huffington Post



The Greywater Showcase is a FREE event hosted by Water Wise Davis in partnership with the City of Davis. Water Wise Davis supports wise water policy, and water conservation, reuse, and capture in the City of Davis and is a working group of Cool Davis.

Greg Mahoney and Jennifer Gilbert, City of Davis

Dick Bourne, Retired, Davis Energy Group and UC Davis, now Cool Davis LINK

Dawn Calciano, Conservation Coordinator, City of Davis LINK

Leslie Crenna, EcoAssistant LINK

Dan Gannon, Everyday Ecology LINK

Bernadette Balics, Ecological Landscaping LINK

Eric Dolan, Homeowner LINK

More Greywater Information

  1. Greywater Laundry System Image
  2. Greywater Resources
  3. Greywater Vendors
  4. Greywater Planning Guide p1and p2
  5. Greywater Laundry System Parts List


Distribution lines for graywater system used for outdoor irrigation. Photo credit Johan Verink.