Is it safe to use rain barrel water collected from your roof to irrigate homegrown lettuces, strawberries, and tomatoes?
The question is so straightforward, and yet the answer has been so murky. In the past, many sources cautioned against this use of stormwater runoff, while some, including Seattle Public Utilities, suggest it’s OK with water collected from some roof types but not others.
As rain barrels proliferate and climate change squeezes summer water supplies, there’s certain to be increasing interest in using roof runoff to grow vegetables and fruits. The problem is that there has been little direct research using runoff to water edibles and checking them for contamination. Photo by Barb Howe
Now data from Australia, where scientists used stormwater runoff to irrigate vegetables, as well as recently released results from the Washington Department of Ecology, which analyzed the pollutants washing off roofing materials, are helping resolve the rain barrel dilemma.
Based on these experiments and others, it appears that rain barrel water is safe to use on edibles, particularly if you adhere to some easy-to-follow advice to reduce exposure to bacteria and other contaminants. Unfortunately, some roofing materials—namely treated wood-shake roofing—release much higher levels of pollution than other roof types and are still too suspect to allow use of the runoff on food. But tests on the stormwater dripping from asphalt shingle roofs find that it’s remarkably clean.
So what exactly do the new data say? Let’s take a look.
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