I looked into collecting rainwater for similar reasons, it turns out that alot of the asphalt shingles
used have anti-mold chemicals in there that can be very toxic in certain concentrations. I changed my
mind in trying it. But I have a small shed that just has a metal painted roof. That's where I'll make my
attempt.
I hope that they are making sure that their collection system does not add toxins...or they process it
to make sure it doesn't have any.