There is no valid reason for believing that rainwater will be clean and
fit to drink.

There is a lot of pollution in the air, and it travels thousands of
miles - around the world in many cases. Consider how much acid rain from
the industrial parts of the nation have caused loss of vegetation and
smog in areas downwind several states away. That is just one of many
types of pollution in the atmosphere. No reason to think that the
pollution is stooped at the border by Customs and prevented from
leaving. Nor pollution from other countries is blocked by Homeland
Security from passing across the nation.

If a cruising magazine wanted to do a shocking story, and promote the
sales of its reverse osmosis advertisers, it would have rainwater
samples collected and tested from around the world.