Most travellers know this rule, but it is a big just one: Do not drink the tap water. Faucet water is not really safe to consume in Cancun, as it's rampant with parasites and likely fatal micro organism, and non-locals are particularly prone to obtaining sick from non-filtered drinking water. https://cancun-trip-tips07306.wizzardsblog.com/31826646/cancun-trip-tips-can-be-fun-for-anyone