How to use greywater to quench your thirsty garden, lawn

Leimone Waite
Master gardeners

Q. I have been under water restrictions due to the drought and have converted my washing machine to be able to use the greywater to water my trees. I have also been collecting my sink and shower water to use. Will using this water on my trees harm them?

A. When trees are in extreme drought, any water is better than no water. However, some detergents, shampoos and soaps may contain excessive salts or chemicals that may harm the soil biome and your plants.

When using greywater, you want to select the appropriate detergents and cleaning products to avoid damage to the environment and landscape plants and trees.

The University of California publication “Use of Graywater in Urban Landscapes in California” advises avoiding powered detergents and chlorine-based bleach products in your wash.

Because the greywater can potentially cause harm to the environment, humans and pets, you want to make sure the hose is discharging onto a thick layer of mulch to avoid runoff.

Another issue with using greywater from the laundry is the back pressure on the washing machine pump. To minimize this, make sure to use a large diameter pipe that contains multiple openings.

Darrell Carpenter is converting his garden in Redwood Valley to native and drought-resistant plants.

Collecting water in a bucket or pitcher in the shower or at the sink as you wait for the hot water is an easy way to save water. Because this is pure water, it can be used to water any plant without concern.

However, if your indoor system uses a water softener, be aware that some systems can add lots of salts to the water during the water purification process. Over time this can damage the soil’s tilth, making it hard for roots and water to penetrate.

Using the grey water from the washing machine, the shower or tub and bathroom sink is allowed in California, but grey water from the kitchen sink and dishwasher is not. This is due to food waste potential containing harmful pathogens.

Greywater is not recommended for irrigating vegetables, which could be contaminated by harmful compounds, chemicals or pathogens in the water.

For more information about greywater systems and designing and setting up your own system, read the University of California's graywater informational at

This publication also has good information on the weekly irrigation requirements of a tree based on the size of the it’s canopy. This is useful even for those who don’t have a greywater system and are just trying to conserve water without damaging their landscape trees. For instance, a tree with a 100 square foot canopy that has medium water needs, which are the majority of trees in our landscapes, requires 62 gallons per week in our inland summer climate.

The Shasta Master Gardeners Program can be reached by phone at 242-2219 or email The gardener office is staffed by volunteers trained by the University of California to answer gardeners' questions using information based on scientific research.