In a small sauce pan bring 1 cup of water to a simmer. Stir in sugar, and remove from heat. Stir until sugar is completely dissolved. Set aside to cool.
In a blender or a food processor puree the raspberries. Pour through a strainer to remove the seeds.
Combine lemon juice, pureed raspberries and syrup mixture in a large pitcher. Add 4-6 cups of water depending on how sweet or tart you want it. Start with 4 and taste to adjust.
Serve over ice.
Notes
Shortcut - Add raspberry puree to 1 1/2 quarts of your favorite pre-made lemonade