The NC study in the OP did not mention a control harvest to collect rainwater without the roofing product contamination. Raindrops form around high altitude particulates, some of which are contributions from coal-fired industrial plants, jet contrails, volcanic eruptions and angel feathers. Without intervening roof pollution, acid rain has produced a lot of crystal clear lakes in the Adirondacks: crystal clear because they are lifeless due to elevated pH. Reinforces the recommendation for water analysis. I believe government subsidies are available for rainwater cistern installation in the Florida Keys, to reduce demand on the pipe from the mainland-maybe this is a partial answer to the increasing scarcity of water in the West.