Rain water unsafe for drinking until treated?

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I eavesdropped a conversation of two guys concerning safety of drinking water and was left wondering if really rain water is safe for drinking. One insisted that rain water should not be consumed or even used for shower until it is properly treated. He opined that with ever increased pollution in the atmosphere, rain water may be contaminated or acidic and may therefore harm someone if used or consumed without purification. I think he was right. Any other opinion?