1Heat 1 cup of the water to boiling. Pour water over tea bags; let steep 10 minutes. Remove tea bags; cool tea.
2Heat remaining 4 cups water to boiling. Stir in sugar until dissolved. Remove from heat; cool.
3In 3-quart plastic container, mix tea, sugar water, lemonade concentrate and vodka. Cover and freeze at least 24 hours.
4To serve, place 2/3 cup slush in each glass and fill with 1/3 cup sparkling water; stir. Garnish with lemon slices.