Speed, power, balance. It is a full body workout.
Absolute nonsense. With your weight effectively diminished in water, you cannot ground yourself sufficiently to transmit full power into a technique, nor is it possible to maintain natural balance/coordination through the techniques, add to this that by removing gravity from the equation diminishes basic core function from the training, and these factors render it a useless activity best left to Van Damme in Kickboxer.
If you want to use water effectively, then get a floatation vest/belt and work your cardio by water 'running'. Originaly a rehab exercise, it is now used increasingly by long distance runners/triathletes, to limit the amount of high impact work in their training. It is exhausting.
And dont forget the obvious action of swimming. HIIT length sprints are fantastic for balanced conditioning.
Doing your strikes/kata in water is no different to 'Aquafit' or water aerobics classes. When you see a lean powerful athlete who credits his attributes to joining the pensioners in the pool on a weekday morning, you let me know