By coincidence, I used FX-50 for the 1st time yesterday with London tap water (chlorine, fluorine, chunks of calcium, godknowswhatelse) and the negs were fine. I think it unlikely that any commercial "big-name" developer will be effected by the levels of chlorine found in normal drinking water. If it was, I'm sure they would say to use distilled. On the other hand, one simple test is to do your next film with distilled and see what you get.

Cheers, Bob.