As a spin-off from the 'make people in water easier to hit' I'll bring you this suggestion.
Make sprinting slightly slower in water compared to current situation.
At the moment water isn't exactly a strategical element it could be, it could be used more effectively to slow down your enemy by building at the shore, so enemies couldn't go that way without being shot.
Also who would want water to be a nice place to be. There's land for a reason.