Combine water, salt, sugar, lemon juice, and lemon halves in large pot over medium-high heat.
Bring water to a gentle boil.
Remove pan from heat and add shrimp. Poach shrimp for 3 to 4 minutes.
When time is up, immediately dump ice into the pot to cool shrimp. Allow to sit for 10 to 15 minutes.
Drain shrimp, pat dry, and move to refrigerator (covered) for at least 1 hour.