Is It Safe To Use Rain Barrel Water on Edibles?

This past weekend I did a couple of presentations at the Minnesota Landscape Arboretum that had nothing to do with growing edible plants. And yet, on the breaks in between the talks, the number one thing everyone asked me about was how to grow something at home that they could eat.

Washing my hands in the bathroom, snarfing a quick sandwich next to my car in the parking lot, struggling to get my PowerPoint to work — it didn’t matter where I was or what I was doing, people really wanted to know things about growing food.

I honestly lost count of how many times I was asked whether it was safe to use water from rain barrels on edibles. Time after time, though, I told people the same thing: I wouldn’t do it. Though there are few studies on what’s in the water inside rain barrels, research has shown that it often contains chemicals from roof runoff and air pollution, as well as bird poo, mold, fungi and other stuff that sounds unappetizing at the very least.

Some people seemed fine with that answer, explaining that they would just use the rain barrel water on ornamental plants, the lawn, whatever. But others clearly wanted to convince me that it was fine to use rain barrel water on edibles as long as they washed the food well before eating it. I’ve heard that advice, too. And perhaps it’s true. But why take a chance, I say. Living beneath the last leg of the flight path to the airport as I do, I can’t imagine what must be on my roof, and it’s definitely not going into my salad if I can help it.

It’s weird how sometimes people ask for your thoughts but then, realizing those thoughts aren’t what they hoped you’d be thinking, they set out to change your mind. All I could tell those folks was that it was, of course, their choice to use their water as they pleased. As I said, the science is sketchy on this question, so it’s really a judgement call on whether you feel comfortable using rain barrel water on your food or not.

One of the biggest factors to consider when making your choice is what your roof is made out of. If it’s made of wood shingles, for example, it was likely treated with arsenic or other chemicals to make it resistant to things like moss and rot. Asphalt shingles can be problematic due to the presence of various hydrocarbon compounds. There is some data available on the heavy metals and other chemicals that have been detected in rain barrel water. But because test results vary by location, weather, roof type and so many other things, there doesn’t seem to be any hard evidence on which to base a decision.

If you do opt to use water from rain barrels on edibles, however, there are some things you can do to minimize potential safety issues: (1) Water the soil around edibles without letting the water come in contact with plant leaves, stems and fruit.  (2) Drain your rain barrel regularly and rinse it out well if it smells murky or musty at all. (3) Consider adding a “first flush” system to your rain barrel to divert the initial, most contaminated runoff from the roof.