First time going out of the country

So this is my first time going out of the country and staying at an all inclusive. I have some questions… I’m staying at the Excellence Coral Playa Mujeres. First off, I know that you’re not suppose to drink the water in Mexico and to only get bottled water. But if I’m just brushing my teeth can I use the tap water lol? Can I ask for ice in my drinks? Also, what about tipping? Do I tip with USD or pesos?