Does rain ever fall as pure water? © Getty Images

Does rain ever fall as pure water?

Dirty raindrops keep fallin' on my head.

Asked by: Clive Daniel, Trowbridge

Advertisement

No. Water is an excellent solvent and rain always contains dissolved gases from the atmosphere.

Even in a remote, pollution-free region, rainwater will still be slightly acidic because carbon dioxide in the air reacts with water to form carbonic acid.

Rainwater isn’t even pure when the raindrop forms, because each drop precipitates around a speck of dust, or an airborne bacterium.


Advertisement

Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.