we were very leery!!!!, on the port, there is fat tuesdays... a solid 'rita place (ya know those rita's are made from iced water)... well the huge group of people from the ship had no problem, we didn't either. we also ate there, salsa and who the heck remembers. plus the bar right across the way, fat tuesdays on the left as you enter, this bar on the right, we drank 'rita's here and ate as well. Plus an excursion, it's fuzzy now, playa sol? great beach break where all drinks, except bottled beer included. we even drank draft beer and ate there., people looked at us like we were nuts for drinking draft as they paid for the bottled beer.... we won!, free beer, no illnesss!
so I'm making a HUGE assumption, that the $$$ they get are of such great value that poor sanitation and water quality would immediately X them off the cruise ship highlights. It seems, where ever is high tourism and high demand it is safe.... that' s what we found to be true.... no promises to you though.
ps. my uncle gets the Mon. revenge EVERY time he sails the mexican riveara, my aunt always fine, which does point out that everyones gastrointestional system handles things a bit differently... However he may be the odd man out here, I've never sailed there, just fyi, on the grand scheme of things... but that silly uncle STILL travels each year there so I guess he feels its worth it !!!!!!