Combine water, rhubarb, Gentle Sweet, and Stevia together in a saucepan. Cook for 10 minutes. Cool. Juice 3 lemons. Set aside. In a blender jar, blend the rhubarb mixture with an additional 2 cups of water until smooth. Pour into a gallon picture. Add lemon juice, water, and ice to fill the picture. Serve with lemon slices as a garnish. 1 gallon Rhubarb Lemonade.