Waterwalking is an effect which gives the target the ability to walk on the surface of water for the duration of the spell.
In vanilla Skyrim, it is only found as an ability of certain NPCs, such as the flame atronach and is not available to you as a spell, potion, or enchantment. However, if Dawnguard is installed and you become a Vampire Lord, you will have a constant waterwalking effect while transformed. If Dragonborn is installed, then there is one unique item and a potion with the effect available (but it still cannot be used in custom enchanted items or potions).
Artifacts and unique items that use the effect but cannot be disenchanted include: