Add the water, sugar and blackberries to a 5 qt or larger slow cooker.
Use a potato masher and mash the blackberries in the liquid.
Cover and cook on HIGH for 2 hours.
Turn off the slow cooker and allow the liquid to cool completely.
Using a cheese cloth, strain the liquid to remove all the seeds and bigger pieces of fruit. You want to make sure you get as much of the fruit juices out as possible.
Once the juice has completed drained through the cheese cloth, add in the alcohol and stir.
Add the beverage to glass jars with lids and store in and store in a dry dark place for at least 30 days.