Im thinking about this water thing further, whilst I drink my pollutant laden wake-up cup of coffee.
As far as the photographic process goes I dont believe water quality is that important! Certainly it has to be reasonably neutral, so that rules out the acid rain. The nearer the Ph is to 7 the better, but provided its drinkable its o.k. I imagine the important thing here is consistency. As for dissolved solids, apart from making up pyro developer, I dont know that its worth the trouble of using distilled or excessively filtered water for print making film developing, at least the final wash, needs water free of junk. Thats the only reason I use Tescos instead of tap water for my final film wash.
Incidentally, and on a slightly different tack, I wonder how many of us simple hang our negatives from a line to dry, where they gather airborne dust and debris in the process? Now thats an area where I could improve, and thereby reduce my spotting time.