When you blowdry your wet hair where does the water go?

The vast majority of the water that is present in your wet hair evaporates due to the high temperature provided by the blow dryer. Evaporation is a process by which liquid molecules acquire enough kinetic energy to overcome the forces of attraction that hold them together and escape into the atmosphere. In the context of blow drying hair, the heat from the blow dyer causes the water molecules present in your hair to gain kinetic energy, breaking the hydrogen bonds between them and allowing them to escape into the surrounding air, turning into water vapor. This is the reason why you can observe steam rising from your head when you blow dry your hair.