Other than controlling the movement of water, Aquatians can change the form they take. Aquatians have total control of their human appearance and often carry along pieces of clothing with them through the water in case they have to interact with humans. The only limit to an Aquatian’s human form is that they can not shed or gain mass.

Edit: Realized that I should also add that while Aquatians have more control over their powers in their original form, their human form is their only defense against psychic elements, hence the change in form.