Wash or defrost berries. Place berries in saucepan with water. Bring to a low boil over medium-high heat; simmer until berries begin to pop (about 15 minutes).
Remove saucepan from burner and drain berries in a cheese cloth-lined sieve or juice bag over a large, glass bowl. Crush the cooked berries with a potato masher to release the additional juice.
If using juice as a beverage, sweeten to taste with up to 1 cup sugar; return to saucepan and heat for 2-3 minutes until sugar is dissolved. Remove from burner, cool, and refrigerate (Note: juice can also be canned or frozen for future use).