Water Wise Davis, a working group of Cool Davis, and Tree Davis, a Cool Davis partner, hosted a 5th annual Greywater Showcase online via Zoom on Thursday, July 29, 2021. This year’s showcase focused on trees with special guest speaker Don Shor, owner of Redwood Barn Nursery, and host Larry Guenther, both Tree Davis board members. Leslie Crenna of EcoAssistant presented on the basics on greywater as usual but this year added new slides telling the story of a new innovative first story slab shower system, and how she and Don Shor had been learning from each other about how best to meet tree watering needs with greywater. The program ended with a Laundry to Landscape parts kit giveaway.

Frances Andrews was Q&A moderator and read the land acknowledgment; Chrissy Backman provided program and technical support. Water Wise Davis gives special thanks to all these folks as well as Bernadette Balics, who contributed to the development of the informational handout with specifics about which greywater system is best for what kinds of trees and plants.

Watch the videos here: https://youtu.be/yBKOqkVDwQo

Local water resources updates

City of Davis Conservation Coordinator Dawn Calciano reported that we are in our second dry year and a call was issued July 8 for a voluntary 15% reduction statewide in water use compared to 2020 levels. Dawn also reported that Davis has met its goals for per capita usage, currently at 132 gallons per person per day including outdoor irrigation uses. She believes that turf conversions have made a huge difference in water usage since the 2013 baseline year, which was established during the previous drought cycle.

Dawn emphasized that residents should fix any leaks as soon as possible, keep showers under five minutes using shut off nozzles on hoses, and take cars to carwashes that recycle water. She also pointed participants to two new webpages on the City site that make trees and watering trees a priority and emphasized a major lesson we all learned from last drought: don’t forget to water your trees (even if you stop watering your lawn)!

To determine if you have a leak, Dawn encouraged participants to sign up for AquaHawk! AquaHawk allows you to directly monitor household water use on an hourly basis (with about a 24-hour delay in reporting), so it’s a great way to determine if you have any leaks. If your report shows continuous water usage throughout the day and evening, you mostly likely have a leak. Outdoor irrigation systems are a common source of leaks. Toilets are often a significant source of water waste, too: if you can hear water trickling more than a few minutes after flushing, something is wrong! You can use your own two ears to determine this one!

With 6,200 households currently signed up for AquaHawk, nearly half of Davis is already in the loop. Other Yolo County municipalities also have AquaHawk services including Woodland.

Link to the presentation slides

More City links:



Don Shor

Back in the 1980s just after a profound drought, Don says “People were installing greywater systems themselves and coming into my garden center and asking where should I put this outflow?”

“Then as now, the concerns are the same, the opportunities are greater, and now you have professionals to install these and there are actually building codes.” … “We know a lot more about what plant materials will be successful at or near greywater and those that might be a problem.”

Some tips and rules of thumb follow:

  • Plant trees and woody plants “up” high enough that water flows away from the trunk
  • Water trees deeply once per week!
  • Allow the surface (and soil) to dry out between waterings (except for water tolerant species)
  • Make sure that greywater outflow (mulch basins) are away from the crown of trees
  • Stone fruit and nut trees may do very well with greywater depending on the rootstock and greywater system type
  • Good species for shower greywater systems include coast redwood, crepe myrtle, and ginko
  • Apples, pears, and quinces, passionfruit, and loquats benefit from extra irrigation, and are reasonably resistant to crown rot
  • Most riparian and some southwestern species are tolerant of daily watering
  • Grasses, reeds, sedges, and bamboo can take daily watering
  • Many California natives are particularly susceptible to overwatering and crown rot, and may not be a good fit for greywater, especially a shower system
  • Oaks are a special concern; very vulnerable mature oaks should not have any new irrigation added, likely red buds and lavender as well
  • Citrus is susceptible to crown rot depending on the rootstock so shower systems may not be a good fit
  • Denser soils and clay soils need to consider that greywater is going to stay in the soil longer, and there is a higher likelihood of retaining moisture around the crown of the plant (Stonegate, Covell park, Binning tract all have heavy clay soils)
  • Water molds develop in warm and wet conditions (overwatering in the summer)

Link to the presentation slides

Leslie Crenna

Leslie (yours truly) opened with “The Water Song” from Alicia Murphy to give participants a moment to stretch, take a break, and do the poll. Leslie is a certified Level 2 greywater designer and installer and member of event host Water Wise Davis.

She covered the concept of site-based management of water resources where homeowners play a greater role in not just mindful conservation of water but also those stretch goals of rainwater infiltration and greywater re-use. Greywater, as defined by California code, is water from clothes washers, showers and tubs, and bathroom sinks, which, if re-used on site, offsets potable water use and leads to healthier shade and food producing trees, among other important benefits.

Laundry greywater systems can use the pump in your washing machine to irrigate outdoors, while shower systems must rely on gravity, therefore more trenching, and cost a bit more. Greywater friendly soaps must be used to avoid damaging plants and soil ecology and some scenarios can make greywater much less feasible. Greywater is discharged into excavated basins filled with wood chips around the drip of trees and other larger plants, generally. A 3-way valve is required to allow residents to re-direct water to the sewer if any bleach toxics are used.

On the plant watering needs side of things, Leslie emphasized that acid loving plants do not do well on greywater alone (which is on the alkaline side) unless acid amendments are already part of the plan. Like Don, she mentioned that some plants will absolutely love “wet feet” and the daily water of a shower system like redwoods, bamboo, some vines, some stone fruits depending on rootstock and other conditions, perhaps apples, figs, pears, and persimmons as well. Laundry greywater systems are likely great for most plants, except those that require daily water like certain riparian species. Laundry greywater systems are good for citrus trees, but shower systems likely are not.

A final rule of thumb? Drought tolerant plants with low water needs are best irrigated with drip systems on a timer and not greywater.

Link to the presentation slides

Two laundry greywater kits courtesy the City of Davis were given to two lucky attendees along with a free professional site visit. If you didn’t win this year, you can always try again next year!


To watch the presentations on video, visit the Cool Davis YouTube site

Watch Part 1: https://youtu.be/8FltcoUtgu4

0:00 Welcome from Larry Guenther, Tree Davis board member

5:12 Dawn Calciano, City of Davis Conservation Coordinator, Water Updates

20:20 Don Shor, Tree Davis board member, Greywater in the Landscape

Watch Part 2: https://youtu.be/yBKOqkVDwQo

Leslie Crenna, Water Wise Davis and EcoAssistant, Basics of Residential Greywater