1. In a medium saucepan, cook 3 3/4 cups water and sugar over medium-high heat, stirring, until sugar has dissolved, about 1 minute. Stir in lime zest and juice, tequila, and orange juice. Season with 1/4 teaspoon salt.

2. Pour mixture into a shallow dish; cool, then cover tightly with plastic wrap. Freeze until set, 6 hours or overnight. Using the tines of a fork, scrape mixture until flakes form. Freeze (covered) until ready to serve. Garnish with lime wedges, if desired.