I got very sick from drinking (well-boiled!) water when i was desperate on an island in the Caribbean for some water. For the next 3 years I had horrible gut issues and was basically told by a doctor that there's only management and not really any cure for it.

Then I heard about this probiotic bacteria called limosilactobacillus reuteri which was implicated in a bunch of studies as something that they used to find in people's guts back before processed food really became a huge thing and all these very clear links to a variety health effects (I'll just link the wiki page) [1]. When I went to the store it was the most expensive on the shelf, 40$, but I figured why not and got a couple of them. Haven't had any gut issues since.

I think there's worse things you can do to your guts than using the right probiotics for sure.