1Bring the water to a boil in a very large pot. Squeeze the lemon juice into the water, then throw in the halves. Add the onion, garlic, salt and crab boil. Reduce heat to a simmer, cover, and cook for about 10 minutes.
2Add the potatoes and sausage; cover and simmer for 20 minutes. Add the corn and cook for 10 minutes. Remove from the heat and stir in the shrimp. Let sit covered for 5 minutes or until shrimp are pink. Drain, and serve with melted butter for dipping. Broth may be reserved and reused for cooking rice or other soups.