In a medium saucepan, mix the blueberries with the sugar, water and lemon juice. Simmer over meduim heat until the blueberries begin to burst, about 8 minutes, until the juices of the berries have released and made a sauce. Take about 1/2 cup of the berries and pulse in the food processer and return to sauce. Remove from the heat and toss in a few extra berries; cool. Refrigerate before serving.