- Author: Help Desk Team
Q: Can I use the graywater from my washing machine to water my vegetable garden and fruit trees?
A: There are two key considerations, discussed below, relating to the use of graywater in the garden: what is meant by the term graywater and on what plants to use it.
Graywater Definition
Graywater is untreated, non-disinfected household wastewater that does not include toilet waste. It may be sourced from showers, baths, and washing machines. Untreated water from sources such as kitchen sinks and dishwashers, which may have properties that encourage pathogens, is called dark graywater. Water from toilets and washing machines used to launder diapers or chemically contaminated clothing is called black water. Only graywater should be used in the landscape.
Graywater Usage
Graywater can be safely used to water landscape plants and orchard trees. Because graywater can contain bacteria and viruses that cause illness, it should not be used to grow vegetables if the edible portion may come in contact with the soil. For example, graywater should not be used for growing asparagus, beets, carrots, cucumbers, lettuces and other salad greens, garlic, onions, potatoes, melons, squash, bush beans, radishes, turnips, unstaked tomatoes, or strawberries. Crops not touching the ground like staked tomatoes, peppers, and eggplants should be OK.
https://ccmg.ucanr.edu/files/289340.pdf
Laundry Detergent Considerations
When using laundry rinse water to irrigate plants, your choice of household products will affect the composition of the graywater. The wrong products can adversely affect plants and soils. It is best to avoid using products that contain sodium or sodium compounds, bleach, or boron, as these can result in an alkaline soil condition that suppresses healthy soil biologic activity and is poorly tolerated by many plants.
Although the UC Master Gardener Program of Contra Costa County cannot recommend any products, the FAQ page on Greywater Action's website (https://greywateraction.org/greywater-faq/) lists some products that are plant friendly. These are generally biodegradable, non-toxic, and salt and boron free. The Ecology Center in Berkeley has also evaluated several cleaning products for compatibility with graywater systems. Consult their website at https://ecologycenter.org/factsheets/ for a current list of products. (Click on the link to Greywater-Compatible Cleaning Products.)
Other Considerations
Some key takeaways excerpted from our Marin Master Gardener colleagues are listed below. https://marinmg.ucanr.edu/BASICS/CONSERVE_WATER_-_ENERGY/Graywater/
Do:
Water ornamentals with graywater which is often rich in nutrients.
Check your plants first—Acid-loving plants won't tolerate salts found in high pH graywater and evergreen trees are often more salt-sensitive than deciduous trees.
Alternate graywater irrigation with fresh water to minimize salt build up.
Watch what you put in the wash. Use biodegradable pH balanced, sodium-free, boron-free, chlorine-free products in the washing machine and for bathing.
Apply graywater directly to the ground—don't allow it to be sprayed on plant surfaces.
Use graywater within 24 hours after collecting to minimize bacterial growth.
Don't:
Don't let graywater come in contact with skin.
Don't use on root vegetables such as carrots and onions.
Don't use on lawns unless the graywater is delivered below the surface. If sprayed on the surface, people or pets may come in contact with it.
I hope this helps. Please don't hesitate to contact us with any further questions. Good luck with your tomatoes and fruit trees!
Help Desk of the UC Master Gardeners of Contra Costa County (GD)
Help From the Contra Costa Master Gardeners' Help Desk
Request: I'd like to reduce the use of tap water to irrigate my garden by recycling water from our washing machine. I understand this recycle/reuse water is called "graywater". Could you provide me some guidance on how to use graywater for my garden?
Response: Thank you for contracting Master Gardeners' Help Desk about using graywater in your garden. It's important that we learn how to use water more efficiently as drought conditions continue. I applaud your desire to use graywater as a tool to optimize our finite water resources. However, the use of graywater does come with some challenges.
Graywater is untreated waste water from clothes washers, showers, bathtubs, bathroom sinks and laundry tubs that is used for outdoor watering. In California, graywater does not include waste water from kitchen sinks, dishwashers, toilets, or laundry water from soiled diapers.
Graywater is also an option for irrigating your ornamentals but it should not be used to water root vegetables or any vegetables whose plant parts come into contact with the soil due to the potential that human pathogens might be present.
For more information on graywater installations, see the East Bay Municipal Utility District website http://www.ebmud.com/sites/default/files/pdfs/Graywater%20Fact%20Sheet.pdf and
https://www.ebmud.com/water-and-wastewater/water-conservation/watersmart-gardener.
When using graywater to irrigate plants, you should avoid using household products that contain sodium or sodium compounds, bleach or boron, as these can adversely affect plants and soils resulting in an alkaline soils condition not well tolerated by many plants. The UC article "Using Household Wastewater on Plants" http://vric.ucdavis.edu/pdf/fertilization_Householdwastewater.pdf describes the effect on plants of using products which contain boron and chlorine. The Greywater Action website http://greywateraction.org/contentgreywater?friendly?products/ provides a list of products available that are phosphate, sodium, chlorine and boron free. Although we can't recommend any specific brand, Greywater Action considers the following laundry products graywater friendly: Oasis Liquid Laundry Detergent, ECOS liquid detergent, Vaska and Dr. Bronners liquid soap. The Ecology Center in Berkeley also evaluated a number of laundry products for compatibility with graywater systems and the results are listed on their website: http://ecologycenter.org/factsheets/greywater?cleaning?products/ .
I hope this is helpful. Please feel free to contact us if you have any additional questions.
Thank you for doing your part to conserve water.
Contra Costa Master Gardeners' Help Desk
Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/