Combine the blueberries, sugar, and 1 cup water in a small saucepan.
Bring to a boil over medium-high heat and cook for 5 minutes, gently crushing the blueberries as they soften.
Remove from the heat and pour the mixture through a fine-mesh strainer.
Press gently on the berries to extract the juice, then discard the remaining solids.
Let the blueberry syrup cool to room temperature, then refrigerate until chilled.
Pour the pink lemonade and cold water into an 8-cup pitcher.
Add the chilled blueberry syrup and fresh lemon juice.
Stir well until evenly combined.
Refrigerate until thoroughly chilled, or serve immediately over ice if everything is already cold.
Add fresh blueberries and thin lemon slices to the pitcher or individual glasses.
Fill glasses with ice and pour in the lemonade.
Garnish with fresh blueberries and a lemon slice.