In a medium saucepan, add the water, sugar, and blueberries. Give it a stir. Bring them to a boil, and reduce the heat to low.
Simmer the blueberry mixture for 10 minutes, stirring occasionally to prevent it from sticking or burning. After ten minutes, the blueberries will have partially dissolved, and the syrup in the pot will have reduced in volume. Turn off the heat.
Make a slurry in a separate small dish by combining the cornstarch and the 2 tablespoons of water. Mix it well and add it to the pot. Stir it into the blueberry syrup and let it sit in the pot for 5 minutes.
Serve:
Serve it as is, with blueberry tidbits, or transfer the syrup to a blender and blend it until smooth.
Store:
Store the syrup in a jar with a lid. It will keep in the fridge for one to two weeks. Let it come to room temperature before serving or warm it lightly in the microwave.