The primary cause of water evaporation is energy from the sun. The sun's energy heats up water in oceans, rivers, lakes, and other bodies of water, causing some of the water molecules to gain enough energy to transition from the liquid phase to the gaseous phase (water vapor).
While ocean waves and other factors can influence the rate of evaporation, the main driving force behind the process is solar energy. Microwaves in the atmosphere can also contribute to some heating, but the sun's direct radiation is the most significant factor in the evaporation of water.