1. Combine water and sugar in a small saucepan. Bring to a boil; boil 3 minutes, stirring until sugar dissolves. Remove from heat. Place pan in a large ice-filled bowl until syrup cools to room temperature (about 10 minutes), stirring occasionally.
2. Combine syrup, tequila, lime juice, and liqueur in a pitcher. If desired, rub a lime wedge around rims of 12 margarita glasses, and dip rims in salt. Place 1/2 cup crushed ice in each glass. Pour margarita mixture evenly over ice. Garnish with lime wedges, if desired.