Yes, that is the wire frame underground on/off button.

I have always left it on.  It does not effect the render as far as I know. 

I don't think we are getting the right information to help you.  "... want to add more behide the water..."   are you doing an underwater scene and want to place objects below the water plane?

You will have to click "underground on" to see any object below the default horizon line in wire frame. 

I just referred to Susan Kitchen's book and verified there is no effect on a scene other than being able to view wire frames below the horizon plane.  If that is the button you clicked and your wire frames are now hidden, just click it again and they come back into view.  Okay?