If I go out drinking here at home my body gets a bit iffy the next day, so can't really expect it to be any different in Mexico!
I'm pretty sure the water is fine, however, I got my first dose of food poisoning on our last trip a couple of months ago. There is no way to pin point exactly what I ate that made me sick. Doctor said it probably wasn't the water, but more than likely something I ate. So just be cautious about raw fruits and veggies and stuff that may not have been washed properly