"Don't store it!"
If you ask an Italian, the answer will be “you don’t store it”, meaning that mozzarella should be eaten the same day you get it. Naturally, you can eat it the day after but to taste mozzarella at its best, you should eat it fresh and at room temperature. If you buy it loose, you should leave it in its liquid (the whey) right until the moment you decide to eat it. Never put it in the fridge: if the outside temperature is very cold, put it in a bain-marie of warm water for a few minutes to fully enjoy its flavour.