Measure out the blue raspberry puree into a blender jar.
Add granulated sugar to the blender to enhance sweetness and help with freeze texture.
Squeeze fresh lemon juice into the mixture to add a bright, tangy note that complements the fruit's flavor.
Pour in water to thin the mixture slightly, aiding the blending process and texture formation.
Secure the lid on the blender and blend on high speed until the mixture is bright purple-blue, smooth, and frosty, about 30 seconds.
Once blended, pour the icy mixture into glasses, using a spoon to help distribute the frozen parts evenly.
Serve immediately with a straw or spoon to enjoy the thick, cooling texture and vibrant color.