Rinse the cranberries. Place them in a large saucepan with the water and bring to a boil. Boil for about 5 minutes, or until the skins have burst.
Meanwhile, line a colander with cheesecloth. When the cranberries have burst, strain the juice through the colander, letting it drip into a bowl for a few minutes. Then gently press the cranberries to extract the remaining juice. (If a very c