In a saucepan over medium heat, combine blueberries, water, and sugar.
Bring the mixture to a simmer and mash berries gently with a spoon.
Continue simmering for 10–12 minutes until it thickens slightly.
Strain the syrup through a fine mesh sieve into a jar.
Stir in vanilla extract or other flavorings if using.
Let cool completely, then refrigerate for up to 2 weeks.
