Wash the fruit. Cook the rhubarb in the water with the sugar over low heat until soft. When soft, lift the rhubarb out of the juice and then boil the strawberries in the juice for 2 minutes. Take out strawberries.
Arrange rhubarb and strawberries in layers in a bowl.
Stir the cornstarch with the cold water until smooth. Stir into the hot juice and let boil 2 minutes, stirring constantly. Pour over the fruit.
Serve hot or cold with cream. Serves 6 to 8.