i use rainwater for my indoor dwc grow. the water coming off my new owens corning shingle roof has a ppm of 70 and a ph of 7 and i'm trying to figure out what that may be. the water coming off the old roof was barely 20ppms and a ph of 5.5. i let several rain showers wash it off before i started collecting again. the only thing i could find online is that shingles are made from asphalt and mica but i'm sure there's lots of other chemicals involved