Add the cleaned blackberries and sage to a pitcher and muddle. You can use a wooden spoon for this if you don't have a muddler that's long enough. This will break open the flavors in the berries and the sage and allow them to infuse the water.
Add in ice.
Fill the container with cool water.
Serve chilled.
You can also make this by the glass by using a few leaves of sage and about 5 blackberries. Muddle and then fill with ice and water.