Is rainwater safe to drink?

Dear Tom,
Is rainwater safe to drink? I've heard that it is pure, but I wonder about
it.
John Koldinger
Dear John,
We receive this question frequently, and your skepticism is warranted. Even
ignoring the effect of atmospheric pollution, meteorologist and former
Chicagoan Dr. Keith Heidorn tells us it is a misconception that raindrops
are pure.
Referring to condensation nuclei, Heidorn says, "The fact is, rain would not
fall without some degree of impurity in the air to act as a seed. This seed
may be a chemical salt, an acid droplet, a speck of dust or soil, or even a
bacterium."
Consider also that every cloud droplet begins as moisture condensing onto a
tiny airborne "nucleus." Because a raindrop might consist of a million or
more individual cloud droplets, it is likely that each raindrop contains the
material from a million or more condensation nuclei.