I don’t feel like water is watery enough. Visually, it looks fine, until you drive a car into it. I believe a splash effect and maybe underwater bubbles could make flinging cars into water more visually pleasing.
This comes up every once in a while and I believe the answer last time was "not high on the priorities list" or perhaps "would require too much computing power", though I don't remember.
For me bubble particles from the exhaust while underwater would be enough (unless the engine is not running, of course!)