Bring the water to a boil in a large saucepan. Add the shrimp and cook until just pink, no more than 3 to 5 minutes. Drain well and rinse in cold water to prevent further cooking. Peel and devein shrimp, leaving tails on. In a large glass airtight jar (about 1 1/2 quarts *) layer shrimp and onions and top each layer with ground black pepper, peppercorns, bay leaf and a clove of garlic. Keep layering until jar is about 2/3 full. Pour vinegar and lemon juice over layers until jar is almost full. Leave space at the top so you can gently shake jar to remix ingredients. Seal jar tightly and chill for a few days up to 2 weeks. Turn jar upside down to remix every other day or so. Serve chilled as an appetizer.
* Note: for larger shrimp you may need a larger jar and adjust ingredients accordingly.