Anything that can cut down on the preparation time before cooking is a plus. Sometimes, it might better suit your schedule to peel and prepare your potatoes a few hours or the day before you plan to cook them. You can keep prepared potatoes in water in the refrigerator for up to 24 hours. If you don't keep them in water, they'll turn brown.
Peeled or cut raw potatoes turn brown when they are exposed to air for too long. Keeping them in cold water until you are ready to cook them helps them look their best. Although brown potato flesh isn't attractive, it's still safe to eat. Peel and cut, slice or dice your potatoes, and place them in a bowl or pan of cold water as you cut them. Once you are finished, make sure cold water covers every piece. Cover the bowl or pan with an airtight lid or plastic wrap, and place the bowl in the refrigerator. Keep the cut potatoes submerged in cold water, in the refrigerator, for up to 24 hours.