In a small or medium sized saucepan, combine the blueberries, water, and granulated sugar.
Place on medium-low heat and allow to simmer, stirring occasionally, until the blueberries have cooked down and you have a slightly thickened syrup, about 10-15 minutes.
Transfer the blueberry syrup to a food processor to blend as smooth as you can get it, if desired.
If desired, strain the blueberry syrup through a strainer to remove any leftover solids.
Transfer to an air tight container and place in the fridge to cool.
When cool, add a few Tablespoons of blueberry syrup to a glass, and fill the glass with milk. Stir to combine.
Notes
Store blueberry syrup separately from milk, in an airtight container for up to 1 week. Mix together when ready to serve.