01 - Rinse the cranberries thoroughly under cold water.
02 - In a medium saucepan, combine cranberries and water. Bring to a boil over medium-high heat.
03 - Reduce heat and simmer for 10 to 12 minutes, until cranberries burst and soften.
04 - Remove from heat. Using a fine-mesh sieve or cheesecloth, strain the mixture into a large bowl or pitcher, pressing to extract as much juice as possible. Discard solids.
05 - Stir in sugar while juice is still warm, mixing until dissolved. Add lemon juice if desired.
06 - Cool to room temperature, then refrigerate until chilled. Serve over ice.