Peel shrimps leaving the tail sections intact. Using a knife, make a shallow incision down the back of each shrimp. Pull out intestinal tract and discard. In a small bowl, combine shrimp, lemon juice, pepper and 1/2 teaspoon of the salt. Marinate in the refrigerator for about 10 minutes.
In a large bowl, whisk together water and egg. Add flour, cornstarch and the remaining 1 teaspoon of the salt. Whisk together into a smooth batter.
In a large pan over medium heat, heat about 2 inches oil.
Drain shrimps from marinade. Holding by the tail, dip shrimps one at a time in batter to fully coat. Drop into the hot oil and cook for about 2 to 3 minutes or until golden and crisp. Cook in batches as needed. With a slotted spoon, remove from pan and drain on a wire rack set over a baking sheet. Serve immediately with sweet and sour sauce or banana ketchup.
The oil is hot enough and ready for frying when a cube of bread tossed in browns in 1 minute.