Thanks to an awesome program run by my local water department, I am about to get a large downspout planter box. When I mentioned to the guy doing the site assessment I planned to put tomatoes in the planter box, he said that vegetables (or any edible plants) should not be grown in downspout planters. When I pressed him, he didn't have much to say.

So, collective wisdom, is this a good idea or not? The water would be draining from the front half of my house; part of that area has a newer white roof, the other part has traditional flat-roof material. As it is the same rain that falls on my other vegetables, I can't see what the problem would be, unless the roofing materials contribute some contaminant (but since no one tells you not to water your edibles with rainbarrel water, I still am not seeing what the issue is).

Thoughts?