- In a large heavy saucepan, combine blueberries, rhubarb, lemon juice and water.
- Bring to a boil, stirring frequently, reduce heat and simmer for 10 minutes.
- Stir in sugar; turn heat to high and boil vigorously until jam reaches setting point. (218 - 220F), about 10 to 15 minutes, stirring frequently.
- Remove from heat, skim off any accumulating foam and stir for 3 - 5 minutes.
- Fill sterilized jars and seal.