In a saucepan over medium heat, combine the sugar and water, stirring until the sugar dissolves. Add the dried hibiscus flowers and blueberries to the pan, then bring to a boil. Lower the heat and simmer for 3 to 4 minutes. Gently press the blueberries with a wooden spoon to release their juices.

Strain the mixture through a fine mesh strainer into a measuring cup or pitcher, then let it cool.

Once cooled, mix the syrup with the filtered water and lemon juice, stirring well. Refrigerate until chilled. Serve over ice.