In a medium pot, add the water, half white onion, garlic, & salt. Add the shrimp shells, & cook for about 10 minutes. Remove shells after 10 minutes

Chop your tomatoes, cucumber, onion, cilantro & chile serranos into small cubes. (remove cucumber seeds with a spoon)

Add the shrimp to the boiling pot, stirring occasionally for 2-3 minutes.

Transfer the shrimp into a bowl with ice to let it cool.

Whisk ketchup, shrimp broth, clamato, lime juice in a bowl

Add your cilantro, purple onion, cucumber, chile serranos, maggi sauce, and hot pepper sauce in a separate bowl; stir shrimp in.

Chill coctel for at least 30 minutes in refrigerator. Serve in bowls or large seafood cups with tostadas, saltines or tortilla chips on the side.