In a mixing glass or cocktail shaker, combine the fresh blackberries and sage leaves. Use a muddler or the back of a spoon to crush them together gently until the blackberries are well crushed and the sage releases its fragrant oils.
Add the honey or agave syrup and freshly squeezed lime juice to the muddled mixture. Stir gently until the sweetener is fully dissolved and well incorporated throughout.
Take a serving glass and fill it halfway with ice cubes, creating a refreshing base for your mocktail.
Using a fine mesh strainer, strain the berry-sage mixture over the ice in your serving glass, ensuring that any solid bits are caught, resulting in a smooth beverage.
Slowly pour soda water over the top of the strained mixture, allowing the bubbles to mix gently. Stir the drink with a spoon to combine the flavors without losing carbonation.
For an appealing presentation, garnish your mocktail with a few extra blackberries and an elegant sprig of sage placed atop.
Notes
Serve in a tall glass for an appealing look. A lime wheel can be added for extra color.