Combine the cranberries and water in a large saucepan.
2
Bring to a boil over medium-high heat, then reduce the heat and simmer for 15–20 minutes, until most of the berries have burst.
3
Remove from the heat and let cool slightly.
4
Strain through a fine-mesh sieve into a bowl or pitcher, pressing the berries gently to release their juice; avoid pressing too hard if you prefer a clearer drink.
5
Stir in the sugar and lemon juice, if using, until the sugar dissolves.
6
Taste and adjust the sweetness, then chill before serving.