This is an important issue. In reading around the pet forums I belong to, I see more than a few people use distilled water to "avoid urinary tract problems". Some say their vets told them to do it. If only these vets would tell them to feed a canned only diet instead. Some say they read it on the internet.
I'm not big on chemistry but this info about distilled water makes sense to me, and I will continue to share the link in the hopes of educating a few more.
None of my cats drink water at all now, being all canned kitties. I used to add water to their canned food, but as my water is hard well water (heavy minerals) I really think that was at least part of the problem for my FLUTD kitty. The other cat I was adding so much water to her food to slow her down and help her feel filled, I discovered had a consistent urine pH of 6.75, so I've reduced the amount of water I add to her canned food now too.
PS I want to clarify that I always have their bowl of water available, freshened several times a day, even though I never see any of them drinking from it.