Combine thawed rhubarb and strawberries in bowl, juice and all. Pour into 9x13 pan. Sprinkle dry cake mix over fruit. Cut butter into pieces. Dot top of cake mix with butter. Pour water over dry mix and butter. Bake at 350 approx. one hour. or until cake is nice and brown. No need to frost. I suppose you could sprinkle with powdered sugar if you like. Serve warm or cold.