Study: Bath & laundry wastewater benefit landscape plants


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Before you scoff at this headline — because it sounds gross — read on. Because new research — from the Water Environment Research Foundation in collaboration with the American Cleaning Institute — has found that many plants surrounding your home do well under long-term graywater irrigation. Graywater is water from bathroom sinks, showers, tubs and washing machines — but not toilets.

According to WERF and ACI, graywater makes up nearly 50% of a household’s wastewater and could supply 100% of the residential irrigation demand in some areas of the country.

Greywater Action – For a Sustainable Water Culture is a group of educators, designers, builders and artists who educate and empower people to build sustainable water culture and infrastructure. (They were not involved in the study but offer tons of information regarding the use of graywater.)

According to Greywater Action, even though graywater may contain traces of dirt, food, grease, hair and household cleaning products — and while it may look “dirty” — it is a safe and beneficial source of irrigation water in a yard. And for an added bonus, using graywater is a great way to save water and money. Reusing graywater also keeps it out of the sewer or septic system, reducing the chance that it will pollute local bodies of water. “Reusing graywater for irrigation reconnects urban residents and our backyard gardens to the natural water cycle,” according to Greywater Action’s website.

So how do you use it? Greywater Action says the easiest way is to pipe it directly outside and use it to water ornamental plants or fruit trees. Graywater can be used directly on vegetables as long as it doesn't touch edible parts of the plants. If you’re going to use the graywater system, it is crucial to put nothing toxic down the drain — no bleach, dye, bath salts, cleanser, shampoo with unpronounceable ingredients and products containing boron.

Now back to the study. Researchers tested existing and new household graywater irrigation systems in Arizona, California, Colorado and Texas. While soil irrigated with graywater showed increased levels of surfactants (surface active agents), antimicrobials and sodium compared with those irrigated with freshwater, only three salt-sensitive tree species (avocado, lemon and Scotch pine) out of 22 plant species that the study tested negatively responded to long-term graywater irrigation. In addition, results from a greenhouse study showed that nitrogen present in graywater was beneficial for plant growth.

The Arizona site provided the most reliable results, according to the study. Graywater irrigation had positive impacts, including higher shoot growth, better density, color, less degree of winter dormancy and overall quality, on Bermuda grass, peach and black-eyed Susan. Canna lily did not show differences between graywater and control treatments. Graywater irrigation had negative impacts on lemon and hybrid Rose.

Public health concerns about graywater include the potential for exposure to pathogenic organisms after graywater is used for irrigation, according to the study. A primary concern is the possibility of spreading human diseases. “While it is well-established that graywater contains indicator organisms, the fate of pathogens after graywater application is not well understood and their persistence could result in human health risks.”

Click here for the full report, “Long-term Study on Landscape Irrigation Using Household Graywater-Experimental Study.”

Tell us: Would you consider using graywater to irrigate your lawn?