Combine plums, sugar, and water in a large saucepan; bring to a boil. Cover, reduce heat, and simmer 10 minutes. Uncover and simmer 50 minutes or until mixture begins to thicken, skimming foam from surface of mixture occasionally. Cool; pour into an airtight container. (Mixture will thicken as it cools.) Cover and chill.
Note: Refrigerate jam in an airtight container for up to three weeks.