Place the watermelon, raspberries, blueberries and water in a blender; cover and blend until smooth.

Strain through fine mesh strainer into pitcher (you can keep some pulp in the drink if you prefer).

Stir in sugar and lemon juice until sugar dissolves. Refrigerate until chilled, about 1 hour.

Garnish with lemons. Don't try and double this, just make batches.