If I have a cold drink outside on a humid day, I get a lot of condensation on the can. If the can were thoroughly cleaned beforehand, would the collected condensation be potable?
Yep. You’ve discovered the solar still.
In this case, the solar “evaporator” is the environment.
Now, if it were rain, which is also condensed atmospheric water vapor, you’d have to deal with the fact that each drop has a condensation nucleus, which may be a grain of dust or something else you may want to filter out first.
Wouldn’t it have your hand grime on it?
This was the kind of thing I was wondering about. If the water would bring floating particulates in the air with it.
The vapor doesn’t contain anything but water. It’s mixed with the other gaseous constituents of air, but it’s all dissolved together in a big indistinguishable gaseous mixture.
When the water condenses, it’s the only thing in a normal air mixture that comes out of vapor phase at that temperature, so the resulting liquid water doesn’t bring anything out of the rest of the atmosphere with it. At the instant it condenses, it’s about as pure as it can be.
After that, it can begin to dissolve other water-soluable substances or mix with stuff it’s in contact with, like atmospheric gases or dust on the condensation surface, but that’s true of any liquid water anywhere.
What you have is distilled water, which is as pure as you can get water without some moderately (or extremely) exotic purification technology.
You may notice that the air quality index, at least with regards to particulate matter, improves after a rainstorm. The condensation of the initial rain drop around a particle is just the starting point; the droplet also removes lots of PM from the air as it falls thousands of feet down to the ground. This works so well that it’s the mechanism of action in wet scrubbers for cleaning industrial exhaust gas streams:
For condensate developing on your cold beverage can, it will only be collecting whatever PM happens to breeze by it. Which is to say, not much - no more than the free surface of the beverage inside the can itself.