Heat 3 cups water with the sugar in a saucepan over medium to high heat, stirring, until sugar dissolves. Remove from heat and stir in flowers; steep 10 minutes. Strain; add 1 cup of ice and stir until ice melts and mixtures chilled. Pour remaining 4 cups of cool water and the lemon juice into a small pitcher.

To serve, pour about 3/4 cup flower syrup into a tall, ice-filled glass. Top with about 3/4 cup lemon mixture; stir to combine.