I've been using it for years along with collected rain. I certainly don't want to start a debate on this and if you live where there are known heavy pollutants in the air it's probably not good but if it's so bad then how do all the trees grasses and plants not die from it? I would rather dump snow and rain on my plants then bottles of unknown "stuff."
Being down wind of heavy industrial and electric generating plants. Swing's my choice!
I get some interesting results from outdoor soil testing on the farm. FAR, far removed from indoor/home built soils. The major difference, is in those things the falling moisture collects.
In reality, we do have some issue's with the rain and the forest's. In all the forest plants too. Not to mention the Great Lakes and Mercury content.....
Check your local DNR for info on that.
But, I don't feel that choice of yours is wrong either! Maybe not the best around here but, not bad .....
For all MJ growing. I'm partial to RO. I know exactly whats (not) in it.
If I lived on the west coast or central plains to the mountain states. I might be more inclined to. It's simply my choice to not.
It shouldn't be a debate. It's just a choice folks!