Combine the water, orange juice, and sugar in a medium saucepan over medium-high heat. Stir until the sugar dissolves, then bring to a boil.

Add the cranberries and reduce the heat to medium. Simmer, stirring occasionally, for 5 to 10 minutes, or until the sauce is a deep red and the cranberries have popped but still mostly retain their shape. The sauce will thicken as it cools.

Remove from the heat and stir in the orange zest, if using. Allow to cool to room temperature, then transfer to an airtight container and store in the refrigerator until ready to serve.