Drink bottled or filtered water, including the ice question

Tap water isn't drinkable for visitors anywhere in Mexico, and that includes brushing your teeth in some areas. Restaurants and hotels use purified water and ice made from it, so ice in a proper restaurant is fine; the risk is more with raw salads rinsed in tap water at small places. Buy large garrafones of water for your room instead of many small bottles, and carry oral rehydration salts in case.