I don’t know about mineral content… but I’m not sure of the bugs, either.
When I first started working in Mexico, I really, really sick the first night there. Then I was fine for a while. Then I got sick a couple of more times, each time less severe. Now I think I’m immune, and never have problems when I go back there. Of course I don’t eat or drink anything the Mexicans themselves don’t.
When I brought my wife here from down there, I was fully expecting that she’d get sick, too, just from the change in bugs that are floating around. It never happened. I don’t know if she’s just stronger, or if the chlorine in the water alone had an effect, or whether it’s just something else.
I’ll be able to put it to the real test in a couple of days, though. My brother and mother are going down there with us this time – if I don’t get sick and they do, maybe we’ll know something. Of course with such small experimental and control groups, maybe it won’t be valid.