Add the blackberries, water, and sugar to a medium saucepan.
Stirring occasionally, bring to a simmer over medium heat. Simmer for 5-7 minutes, or until the blackberries disintegrate into mostly seeds and cores. Remove from heat.
Strain the blackberry pulp from the liquid, discarding the pulp and reserving the liquid. Stir in the blackberry extract if using (this adds some tartness to the syrup), then allow the syrup to cool at room temperature for 15 minutes.
After cooling time, transfer the syrup to a syrup bottle or mason jar with a lid and store in the fridge for up to 2 weeks.