Place rhubarb into a large soup pot; stir in water and sugar. Bring the rhubarb to a boil and cook over medium heat until rhubarb is soft, about 20 minutes. Stir often. Strain rhubarb and liquid through cheesecloth into a large bowl and discard rhubarb pulp.
Return rhubarb liquid to the pot, place over medium heat, and stir in pineapple juice and strawberry gelatin. Bring to a boil, stirring to dissolve gelatin. Store punch in quart jars in refrigerator.