Cut the onion into half. Dice one part for the dish and save the other for boiling the shrimp. Rinse the diced portion under cold water for 30 seconds.
To cook the shrimp, bring water, garlic, onion chunks, salt, and black pepper to a boil. Add the shrimp, turn off the heat, and let it sit until the shrimp turn pink.
Drain the shrimp and let them cool. Reserve some for garnish, and if they are large, cut them in half for easier consumption.
Combine your liquid ingredients: Clamato juice, ketchup, lime juice, and hot sauce. Set aside.
In a separate bowl, mix the diced veggies, jalapeno, and cilantro. Add in the cooked shrimp.
Assemble in large margarita glasses, pour the liquid mixture over, and serve with lime wedges and cilantro sprigs.