Bring 3 cups water and the sugar to boil in a saucepan, stirring frequently until the sugar has dissolved. Remove from the heat and allow to cool for about 10 minutes. Stir in the lime juice, lemon juice, orange liqueur and tequila. Transfer mixture to a 9 x 13-inch freezer-safe dish. Carefully place in the freezer and mix with a fork every 30 minutes until all the liquid has frozen, about 3 hours total.
If serving in individual glasses, dip the glass rims into water and then dip into salt. Spoon granita into glasses and serve with a slice of lemon and/or lime.
Feel free to serve this granita any way you would like. Got some cute margarita glasses? Go for it!