Sweet-n-Sour Kielbasa

2 pounds kielbasa sausage, cut into 1/4-inch slices

1 (12 ounce) bottle tomato-based chili sauce (such as Heinz®)

1 (12 ounce) jar red currant jelly

1 tablespoon crushed red pepper flakes

½ cup water

Stir the sausage slices, chili sauce, red currant jelly, red pepper flakes, and water together in a slow cooker, cover, and set the cooker to Low. Cook at least 4 hours, stirring once every hour.