Pour the water and beer into your crockpot and stir in the Old Bay seasoning, smoked paprika, smashed garlic cloves, and bay leaves. This flavorful liquid will be the foundation for everything, so make sure the seasoning dissolves well and distributes evenly throughout. I like to give it a good stir to ensure no clumps of Old Bay settle at the bottom.
Add the red potatoes (cut into 2-inch chunks), celery pieces, onion wedges, and lemon halves to the crockpot with the seasoning base from Step 1. Stir everything together to coat the vegetables in the seasoning liquid. These vegetables need the full cooking time to become tender, so it's important they go in early. Cover the crockpot and cook on LOW for 4 to 5 hours.
After the potatoes have cooked for 4 to 5 hours and are nearly tender, add the sliced kielbasa or smoked sausage and corn pieces (cut into 3-inch pieces) to the crockpot. Stir gently to distribute them throughout. Keep the heat on LOW and cook for an additional 2 hours. The sausage will warm through and impart its smoky flavor into the broth, while the corn will become tender.
Increase the crockpot heat to HIGH and add the peeled and deveined shrimp directly to the pot. I like to stir them in gently so they distribute throughout the liquid. Cook on HIGH for 30 to 40 minutes, just until the shrimp turn pink and opaque—don't overcook or they'll become rubbery. Drain the entire contents through a colander to remove excess liquid, reserving some broth if desired for dipping.
Transfer the drained low country boil to a large serving platter or individual bowls. Arrange all the components—potatoes, corn, sausage, shrimp, and vegetables—so everything is visible and appealing. Serve with small bowls of melted salted butter and cocktail sauce on the side for dipping. Garnish with fresh lemon wedges if desired.