what is the right way to install a 6x6 support for a 14' x 20' deck. The water level is only 2'
below grade. Do I dig a hole below the water line. Do I put the wood on a concrete slab. The
deck is only a couple a feet off the ground. Should I dig it down below the frost line.

what is the right way to install a 6x6 support for a 14' x 20' deck. The water level is only 2'
below grade. do I dig a hole below the water line. Do I put the wood on a concrete slab. The
deck is only a couple a feet off the ground. Should I dig it down below the frost line.
I would recommend a footing at least 2' deep and 18" square (with squared corners). Also... if it were me... I would build the footing high enough so that the water won't contact the wood. Install the 6X6 at least 1" above the top surface of the concrete footing.

If the deck is not attached to another building you don't need to worry about the frost line. The deck will pretty much float with the frost.