It seems like we'll be able to drive on water scooters in the upcoming Grand Theft Auto V as Rockstar released this wallpaper. As the scooter is marked "lifeguard" with the person on board blasting away with his gun it would seem reasonable to assume you'll be able to steal and drive them much like any other vehicle in the game.
David Hasselhoff beware, the coastlines of Los Santos are safe no more!