Put the blueberries, sugar and ¼ cup of water in a small saucepan and bring to a simmer. Simmer for around 5 minutes, stirring regularly, until the blueberries pop and the color is bright. Strain through a fine strainer/sieve or cheesecloth and set aside to cool. Can be make ahead.
Add the lemon juice and water to the blueberry syrup and blend until well combined. Chill until needed.
Gently stir before serving over ice - you can add some blueberries for garnish as well.