Here is an advance in my attempts to design drinkable rainwater collecting devices: It is not quite the solution, but on the right track: A section of the roof of a house could be sprayed with glass or something like glass, and the water collected in a drinking water gutter, then stored inside the house or inside the wall, in a tank for drinkable water. An eight or sixteen foot section is all that would be needed to collect five to fifteen gallons from a good rainstorm. Wherever the sky is still clean, rainwater should be safe to drink. One could see what, if any, impurities are in it by evaporating some off, and even test the ph or acidity, to see if it is that of water. Glass is not quite right because it is breakable and slippery, and a rainwater collector would have to be cleaned. But this is the direction experimental designs might go, and it is surprising that these problems have not been solved yet.
On my inventions page, I had hoped to design small people pods as minimal shelter for the homeless and refugees. I hoped that these could be made to collect and store rainwater. It is amusing how much heat or energy and how much water are wasted with the current roofing system of tar shingles, which are designed to solve a different problem.