If anything, I'd expect well water to help Crohn's sufferers. The vast majority of Crohn's patients are in the developed world where most people get chlorinated public water supplies. The less developed countries rely heavily on well water and have a noticeably low rate of Crohn's afflicted people.
As someone already pointed out, public water supplies can be well water. More likely it's from a reservoir, but gets chlorinated and perhaps aerated before being piped to your house.
Mineral content of well water is probably higher than reservoir water. The mineral content will vary due to local geology. A problem in many areas is a high concentration of calcium carbonate, causing so-called "hard water." Drinking that all the time can contribute to kidney stones. If that's a concern for you, add a little lemon juice to your water, but that's not a panacea.
All those fancy designer waters like Perrier are essentially well water, though they'll call it "spring water" for marketing purposes.
I did have a friend some years ago living in Fallon, Nevada (USA) who regularly drank well water which, as it turned out, had a high arsenic content. My friend got very ill from it, and might have died had it not finally been discovered where his arsenic poisoning was coming from. The lesson I took from his experience is that not all well water is equal.
So my conclusion: I actually don't think water quality has much to do with Crohn's. Conceivably, chlorination could have some effect (either positive or negative) on Crohn's, but I've never heard that before and I don't want to spread a rumor that it does.
Post Edited (ozonehole) : 11/16/2013 3:15:20 AM (GMT-7)