This would make some semblance of sense if it weren't for two things:
1) You're not drinking rainwater, I assure you.
2) Sure, the sun evaporates water, and that forms into clouds, and then it rains. Except that things in the atmosphere can taint that rain; this is most noticeable in the form of acid rain: http://en.wikipedia.org/wiki/Acid_rain
There's absolutely no reason to believe that treated sewer water is any less safe than the water that's sitting in your reservoir at all.
1) You're not drinking rainwater, I assure you.
2) Sure, the sun evaporates water, and that forms into clouds, and then it rains. Except that things in the atmosphere can taint that rain; this is most noticeable in the form of acid rain: http://en.wikipedia.org/wiki/Acid_rain
There's absolutely no reason to believe that treated sewer water is any less safe than the water that's sitting in your reservoir at all.