Most travelers know this rule, but it's a big one particular: Usually do not drink the tap water. Tap water is just not safe to drink in Cancun, mainly because it's rampant with parasites and probably lethal micro organism, and non-locals are very susceptible to obtaining sick from non-filtered h2o. https://travisnvyzy.shotblogs.com/getting-my-cancun-trip-tips-to-work-45766271