Irrigating With Graywater
By Andrea Peck UCCE Master Gardeners
How does recycled water affect plants? Lynn, Los Osos
The drought has a powerful effect on us all, causing us to reduce and reuse where we can. But what effect does “already used” water have on your plants? Researchers continue to look at the long-term consequences of graywater on plants and the environment, but one thing remains clear: what you use to water your plants matters.
Graywater includes water from the bathroom sink, bathtub, shower and clothes washer. Black water, which should not be recycled for home use, includes water that comes from the toilet, kitchen sink and dishwasher. Studies indicate that black water may contain high levels of contaminants that can be hazardous to humans and pets.
Graywater, on the other hand, is a little bit of both. Some elements of graywater are actually beneficial--healthy microbes nourish the soil and the phosphates that make up soaps and detergents serve as a plant fertilizer.
However, graywater often contains salts, particularly if your home has a water softener. Salts can build up in the soil and create a barrier that reduces the ability of the plant to take up water.
Boron is another unfriendly addition that often flows with your graywater. Boron is commonly used in laundry detergents and though it is a necessary mineral, it can quickly become toxic. Plants with excessive boron may develop burned spots.
Chlorine bleach kills whatever you throw in its path and will definitely take its toll on your plants.
Despite these roadblocks, there are a number of ways in which you can get the most for your efforts. Make sure you set up your washing machine properly. A basic laundry-to-landscape system is not complicated, but it should include a valve that allows you to switch from sewer or septic and back to landscape. When using detergents, you may choose to use only the ‘rinse' portion of your wash. Refrain from using graywater on potted plants, root vegetables and the edible portion of the plant. Finally, keep a close eye on your plants--you may be the best judge!
For more information about greywater in the landscape visit http://ucanr.edu/sites/mgslo/files/230135.pdf