In a saucepan, combine cranberries, 1 ½ cups water, and sugar. Simmer over medium heat until cranberries burst (about 8–10 minutes).
Strain the mixture into a bowl or pitcher, discarding solids. Let cool.
Stir in fresh lemon juice and the remaining 1 ½ cups of cold water.
Taste and adjust sweetness if needed.
Chill in the refrigerator or serve immediately over ice.
Garnish with lemon slices, fresh cranberries, or mint before serving.