R.Ranger,
A water ground doesn't really provide any great benifit as opposed to other type grounds. If you happen to live in 'wet' areas, or on a boat, it's reasonable to use a water ground and mount your antenna at ground level (which works fine). If you have the option of mounting your antenna at some higher level (the higher the better) then do so. The benifit being that the antenna is able to 'see' much further, longer distance to the horizon.
If you do mount your antenna over water, forget the ground rod and use a radial system in the water, works much better. Radial systems are hugely better for RF than ground rods in any situation. Sometimes the radials are more work than ground rods, but they still are worth it.
- 'Doc
PS - FWIW - Pure/clean water is an insulator. The 'dirtier' it is, more mineral/salt content, the better a conductor it is. The lower the resistance of 'dirt', or water, the better it works as an RF conductor/ground. Dirt or water is never as good a conductor/ground as metal.