Why does water make things wet?

Wetness comes from the balance between cohesion, water molecules sticking to one another, and adhesion, water sticking to other materials. Water molecules are polar, with slightly positive and negative ends, so they are strongly attracted to other polar materials such as cotton, paper and skin, and cling to them. On waxy or oily surfaces, like a duck’s feathers or a lotus leaf, adhesion is weak and the water beads up instead. Scientists measure this with the “contact angle”: a low angle means water spreads and wets, and a high angle means it resists. Whether water itself is “wet” is a popular debate that depends on how you define the word.