In a medium saucepan, cook 3 ¾ 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 ¼ tsp salt.
Pour mixture into a shallow dish, cool, then cover can freeze until set, about 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.