That is a Very Good question BallValve.
Where I live you hit water at 10-12 feet, When we have rain.
I install all my own ground systems, because I live in the country and they don't even maintain there PolePigs. (Transformers are Rusty and leak oil)
My tower Takes Lightning strikes on a normal basis, and I have yet to have a problem with the electronics connected to it.
Now that every thing is put in underground with PVC, You can not even rely on it for a ground.
Have a Great Day.