In a medium saucepan, combine the berries, water, sugar and lemon juice. Bring the mixture to a boil over medium heat, then reduce to medium-low. Gently simmer the sauce, stirring frequently, until it thickens and reduces to about 1 cup, about 20 minutes. Remove from the heat and add the butter and vanilla. Stir until the butter is melted. Serve the warm sauce spooned over plain Greek yogurt, ice cream, biscuits, pancakes, waffles or a simple Angel Food or Pound cake.