Add blueberries, water, and sugar to a saucepan over medium heat. Bring the mixture to a gentle boil, then reduce the heat and let it simmer for 10–15 minutes, stirring occasionally.

Once the berries have broken down and the syrup has thickened slightly, strain it through a fine mesh sieve to remove the solids.

Pour the syrup into a clean, sterilized jar or container.

Let it cool to room temperature, then store it in the fridge.