Raspberry Cordial

Put the unthawed raspberries into the saucepan and add the sugar. Cook over medium heat, stirring once in a while, for 20-25 minutes, until sugar dissolves. With a potato masher, mash the raspberries, and syrup thoroughly. Pour the mixture through a strainer, making sure you extract all the juice. Discard pulp. Squeeze 2 of the lemons and strain the juice. Add to raspberry juice. Boil the 4 cups of water and add it to the juice. Let cool and then chill it in the refrigerator. Serve with thin slice of lemon on top, in each glass.