Have a great trip!
I went to Mexico last summer in late June, and stayed on Isla Mujeres (an island off of Cancun). I've never been in weather that hot before in my life, lol. Florida felt cool in comparison when I came home.
I definitely agree with not drinking the water. Most hotels will provide bottled water for teeth brushing which is nice. Also make sure that if your drink has ice in it, ask if the ice was made with bottled water. I think places are having to do that standard now.