Combine plums, sugar and water in a large saucepan. Bring slowly to a boil, stirring until sugar dissolves. Cook rapidly to gelling point. As mixture thickens, stir frequently to prevent sticking. Remove from heat. Skim foam if necessary. Ladle hot jam into hot jars, leaving 1/4 inch headspace. Adjust two-piece caps. Process 15 minutes in a boiling water canner.

Remove jars from canner with tongs. Leave on counter undisturbed for 24 hours