Add the water, beer, lemon, and garlic to a 12 to 14-quart stock pot (the bigger the better), and bring to a boil.
Add the Old Bay, salt, potatoes, and onions; cook over high heat for 8 minutes. (Throughout this process, you want to maintain a steady boil. If high heat creates too ferocious of a boil, adjust the heat down slightly.)
Add the smoked sausage; continue to cook on high for 5 minutes.
Add the corn to pot; boil for 7 minutes.
At this point, the potatoes should meet little resistance when pierced with a sharp knife. Add the uncooked shrimp in shells, and cook for 3 minutes or until just pink.
Immediately (and carefully) drain the cooking liquid, and then pour the contents of the pot into several large bowls or shallow pails. Sprinkle lightly with additional Old Bay and serve.