Wash the cranberries if fresh and remove any stems and leaves.
Bring the cranberries and water to a boil over medium heat in a large saucepan.
Boil the cranberries for 10 to 15 minutes or until the cranberries burst.
Line a colander with cheesecloth, and place the colander over a bowl.
Pour the cranberries into the cheesecloth and strain until the juice stops flowing out of the colander.
Pour the juice back into the saucepan and add up to 1 cup of sugar, or to taste. Boil the juice for 3 minutes over medium heat. (Optional)
Cool the juice completely before pouring through a funnel into a resealable jar.
Store in the refrigerator for up to one week.