I was in Mexico in 2010 and stayed at the Dreams Tulum resort, and I have booked my wedding for The Now Larimar in Punta Cana. I have been told the water at these resorts do go through a filteration system, but to be on the safe side, I only drank bottled water and used it to brush my teeth as well. Also, eating probiotic yogurt for a few weeks prior to going should help your stomach as well!!!