Use ripe, fresh blackberries for best flavor. Adjust sweetness to taste. For a stronger drink increase tequila slightly. Chill sparkling water and glass beforehand. Strain muddled blackberry juice for a smoother drink. Variations include using vodka or gin, adding fresh herbs, making a frozen version, substituting lime for lemon, or adding a sugar rim. Store leftover blackberry tequila mixture (without sparkling water) in refrigerator up to 2 days.