Hydrokinesis is the elemental ability to create, control and manipulate water in liquid state, levitate ice and a jelly-like substance, as well as break ice, mold the water in an unlimited variety of shapes, and multiply water molecules, creating even more water. With this ability, merpeople can mold the water in the air at will and control the water pressure.
The hand movement for this power is a free flowing hand between a rigid hand and balled-up fist. This may represent the state of water in between frozen and boiled. It may also represent the flowing movements of water and the movement of water molecules in the liquid state. If a mermaid with this power is in the Moon Pool during a special planetary alignment on a full moon, it could be enhanced to aerokinesis.