Add the rinsed and defoliated blackberries to the pot. Pour the water into the pot afterward.
Sift the sugar over the entire surface of the floating blackberries. Turn on the stove to a medium-high setting--325 degrees F on a digital stove.
Cover the pot and allow the berries and sugar to boil for 10 minutes.
Reduce the heat to a low simmer and remove the lid. Mash the berries into the thickening, purple-black sauce with the potato masher. Mash firmly, breaking the berries into the sauce for about 30 seconds. Leave some of the berries intact.
Stir the berries as they simmer for an additional 10 minutes. Remove the pot from the stove and set it aside for use in your cobbler recipe.