01 - Combine cranberries, 1 cup water, and sugar in a small saucepan. Bring to a simmer over medium heat and cook for 7 to 8 minutes, stirring occasionally until cranberries burst and sugar dissolves.
02 - Remove from heat and allow to cool slightly. Strain through a fine-mesh sieve into a large pitcher, pressing to extract all liquid. Discard solids.
03 - Add freshly squeezed lemon juice and remaining 3 cups cold water to the pitcher. Stir thoroughly to combine.
04 - Taste and add more sugar if desired. Refrigerate for at least 1 hour before serving.
05 - Serve over ice, garnished with lemon slices and fresh mint leaves if preferred.