Probably sounds a bit basic, but water is a pretty big deal as far as your skin is concerned. Think of it this way -- like the rest of the human body, skin is composed primarily of water, right? But since it's also exposed to the elements, it can lose that water easily and quickly dry out.
Water is like the fountain of youth for skin, no magical additives needed. It gets some water during showers and baths, but much of the water skin soaks up comes from the inside, meaning you're the one who's in charge of putting it there. And water is very beneficial for skin. For example, it keeps the cells big and juicy, which can help make wrinkles less noticeable. It also works to increase blood flow and clear away built-up toxins. So the more water the better.