How does rainwater become acid?

Answer 1

Rainwater becomes acidic when contaminated water evaporates into clouds and those clouds eventually rain. Water becomes contaminated mainly because toxic, biological, or other waste material are dumped into a body of water like a pond or lake.

Answer 2

Instead of rain, sometimes acid rain falls, this occurs when when the pollution in the air is very high, so when the moisture in the sky collects into clouds, some of that pollution is taken into the cloud form too. When this rains down, you must be very careful, since it's been known to make holes in cars, or their paint.