Place blueberries, sugar and 1 cup water in a blender and process until smooth. Place a fine mesh sieve over a large pitcher and pour the mixture through. Discard the solids that remain in the sieve. To the blueberry mixture, add lemon juice, remaining 3 cups of water and vodka. Stir and taste, add more vodka if desired. Chill until cold. Serve over ice.
Notes
If your blueberries are tart you can increase the sugar to taste.