1. Prepare the Berries: Start by washing your fresh strawberries and raspberries thoroughly. Hull the strawberries, removing the green tops, and then slice them in half or quarters if they are very large.

2. Blend the Fruit: In a blender, combine the hulled strawberries and raspberries. Blend until the mixture is smooth and pureed. This step creates the vibrant color and intense fruit flavor for your mocktail.

3. Strain the Puree (Optional but Recommended): For a smoother drink without seeds, pour the berry puree through a fine-mesh sieve set over a large pitcher or bowl. Use the back of a spoon to press down on the solids, extracting as much juice as possible. Discard the pulp and seeds.

4. Combine with Lemon and Sugar: Add the freshly squeezed lemon juice and granulated sugar to the strained berry puree (or the unstrained puree if you skipped that step). Stir well until the sugar completely dissolves. You might need to stir for a minute or two to ensure no sugar granules remain at the bottom.

5. Add Water and Chill: Pour in the cold water and stir everything together until thoroughly combined. Taste the mixture and adjust sweetness or tartness if desired by adding a tiny bit more sugar or lemon juice.

6. Serve Over Ice: Fill individual glasses with plenty of ice cubes. Pour the strawberry raspberry lemonade mocktail over the ice.

7. Garnish and Enjoy: Garnish each glass with a fresh lemon slice and a few extra whole berries for an appealing presentation. Serve immediately and enjoy your refreshing drink!