In a large saucepan, bring rhubarb, water, sugar and salt to a boil. Reduce heat; simmer, uncovered, for 6-8 minutes or until rhubarb is tender. Stir in strawberries; return to a boil.
Meanwhile, in a large bowl, combine biscuit mix and milk just until moistened. Drop batter in four mounds onto rhubarb mixture. Cook, uncovered, for 10 minutes. Cover and cook 5-8 minutes longer or until a toothpick inserted in a dumpling comes out clean. Serve warm with whipped cream.