In a saucepan over medium heat, combine blueberries, sugar, and 1 cup of water. Simmer for 5 minutes, stirring occasionally, until the blueberries break down.
Remove from heat and strain the mixture through a fine-mesh strainer into a pitcher, discarding solids.
Add fresh lemon juice and 4 cups of cold water to the pitcher. Stir well to combine.
Refrigerate for at least 1 hour to enhance flavors.
Pour over ice, garnish with lemon slices, and enjoy.
Notes
Optional Equipment: A blender can be used for a smoother blueberry syrup.
Customization: Add sparkling water for a fizzy twist.
Storage: Store in the refrigerator for up to 3 days.
Serving Tip: Stir before serving as ingredients may settle.