In a medium saucepan combine cranberries, the water, and maple syrup. Bring to boiling; reduce heat. Simmer 5 minutes. Press mixture through a fine-mesh sieve; discard solids. Return cranberry puree to saucepan.
Remove 1 tsp. zest and squeeze 2 Tbsp. juice from lemon. In a small bowl stir together lemon zest and juice and cornstarch; stir into cranberry mixture. Cook and stir over medium heat until thickened and bubbly. Cook and stir 2 minutes more. Remove from heat. Stir in butter until melted; cool. Store in refrigerator up to 5 days.