Rainwater - is it clean enough?

[JohnA]

there are different kinds of water being used here: tap, demineralised, distilled, what have you...

I've always used rainwater, collected in a water butt from the roof. Due to moss etc I also use a kitchen carbon filter (Britta) to further remove any contaminants. This kind of water is practically free and it's ideal for coolant mix and the like.

My question is: does this sound clean enough to people here?

It doesn't leave any streaks on glass, even when spraying everyday (I also use it to spray my plants in the conservatory, getting more value out of the aircompressor :lol