Place blackberries in medium saucepan over medium heat. Stir in water and sugar and cook until blackberries start to break down. Reduce heat to low; simmer 7 minutes
Strain sauce into a small mixing bowl, using a mesh strainer (squeeze as much juice out as possible by pressing spatula against berries) cool sauce in refrigerator for at least 30 minutes.
To make cocktails, pour lemon juice, ginger ale, riesling and blackberry sauce into pitcher.
Stir well, pour into glasses and garnish with a blackberry and lemon zest
Notes
If you're hosting a casual get together, this cocktail would be super cute served in mason jars!