I train in the water, performing my kata in the pool (autumn to spring) or the surf (during summer). I also lift weights, punch both heavy bags & speed bags, swim laps, & slog the stair-master.
I enjoy working against the resistance of the water. I’d rather not punch air. Timing my techniques in the surf is also entertaining. I find training in the water more effective as I find training in the water more enjoyable. It is training frequently that increases speed & power. I keep just my head above water.
I should note that I am heavy & dense: I weigh 225lbs (16 stone), at 15% Body Fat. I might not be hydrodynamic, but I am fairly waterproof. Other body-types may not enjoy water training as much as I do.