I should note that when I think about getting "sick", I'm talking about "food poisoning". Water can carry anything, for sure, but the "bugs" (heh), that you get from water and the "bugs" that you get from food are somewhat different. If I recall, many of the water borne maladies have longer incubation periods, but with food stuffs, the time is shorter. Also, what I consider food poisoning is usually accompanied by violent vomiting. Not a little upset tummy, or a little vomiting or some diarrhea, but almost explosive vomiting. I've had it and I've witnessed it. Often people feel so bad they get a little worried, as in, "get me to a hospital" worried. Of course, with all this there are many factors wherein some might get a lighter case, but usually, it doesn't matter how strong one's constitution is, if you get a bad food bug, you get sick.
One other note. I'm far more concerned about dirty hands and work surfaces than I am about the water in Cozumel. Same here at home. Most people don't truly understand how to wash their hands or understand that it should be done often. If you get "food poisoning" eating at a restaurant "off the resort", or on the resort for that matter, it's possible that it came from water, but far more probable that it came from dirty hands or a dirty work surface. Those things can happen anywhere, btw.
I drink bottled water in Cozumel, and usually brush my teeth with it, but I also use ice cubes. So..... heh. Also, I eat at a buffet (breakfast) and a restaurant every day I'm in Cozumel, and have for years. It's not that buffets are bad, period, but you have to use a little common sense. The hotel where I stay is quite small. They don't prepare pan after pan of chicken whatever and let it sit around. When they see an item is going, they prepare another pan, fresh. Their steam tables are hot, I've checked. Their buffet is very small.
So, for instance, I've never stayed at or even seen the inside of the beloved Scuba Club Cozumel, and probably never will. Not my cup of tea. But, I'd be inclined to trust their AI food. On the scale, it's not a huge resort, it's smaller. And the thing I think they do really right is that they have people pre order their suppers. They don't need to make enough chicken blah blah and beef laa laa, etc to feed everyone. They have a good idea how many are having the chicken, and how many are having the beef so they're able to "cook to order", in essence. Further, it keeps their food costs down. Smart, and in my opinion, safer.
As to the fruit thing, LOL. I had a friend with me in Playa years ago. We were at a huge AI. They had just under 40 different types of bread, alone, at one of their 3 buffets. He's the kind of guy that sees a buffet as a challenge. 2nd day in, he takes me aside and he's very concerned. "I don't normally really look at this, but, my poop is green." I suggested that it was the gauc he was shoveling into his mouth as fast as he could. Then he got sick. He was queazy etc, and decided that it was bad food or the water. In short, he was constipated from trying to show those Mexicans who could eat how much. He lost 2 days to this. I, on the other hand, made a really, really stupid food decision at the buffet, and got food poisoning. Onset was within 4 hours, in 8 hours I was very ill, and in about 30 hours, I was over it.
Hotel Cozumel is a big place. When you're eating at the buffet, just use some caution and common sense. Don't eat indiscriminately. Oh, and if you ask for water, go ahead and ask for a bottle, but even if you don't, you're going to get one. I've asked local food service people about this. Yea, the water is filtered, but 1. They can charge "money" for the bottled water, and, 2. tourists insist on it. I imagine you can get a glass of water at a restaurant there, some restaurant anyhow, but I've never seen it.
-Blair