- Combine water, beer, potatoes, onions, garlic, lemon, boil-in-bag seasoning, and salt in a 6- or 8-quart slow cooker. Cover, and cook on LOW until potatoes are almost tender, about 4 hours.
- Add sausage and corn to slow cooker. Cover, and cook on HIGH 30 minutes. Transfer corn to a serving platter. Add shrimp to slow cooker; cook, stirring occasionally, until shrimp is opaque and pink, 20 to 30 minutes.
- To serve, drain and discard liquid and seasoning bag. Serve with lemon wedges, cocktail sauce, and melted butter.