Oh, my! I understand your concerns, but Mexico is not another planet. If you are going to tourist friendly areas you certainly have nothing to worry about. While I wouldn't encourage you to drink from the tap because of the taste, I wouldn't recommend you to brush your teeth with bottled water--you would just be adding to the unnecessary waste that is generally associated with American tourists. If you don't want to take any risks, don't eat food off the streets even if you'll miss out on the authentic Mexican culinary experience.

Que disfrutes tus vacaciones!