I've been experimenting with harvesting rainwater by use of portable cisterns and exploitation of naturally occurring drainage patterns...well, actually, I have been moving a 45 gallon trash can under places where water runs off the roof. Fills up fast here in the tropic rainy season.

In looking for information about the potability of rainwater, I stumbled upon a publication from academics that indicates that rainwater is actually poison falling from the skies, and needs to be filtered to 5 microns for removal of lead, and 1 micron for bacteria and parasites.
So much for catching raindrops on my tongue.
This level of filtration is well within reach of my msr miniworks and similar devices, but chlorine, iodine and uv filtration seem to be ruled out.

If the rain is as severely polluted as this, why aren't we all dead?