Gather all ingredients.
Pour water and vinegar into a saucepan; bring to a boil over high heat. Stir in sugar, ginger, chile pepper, ketchup, and garlic; simmer for 5 minutes.
Place cornstarch in a small bowl; mix in water until smooth. Whisk cornstarch mixture into chili sauce.
Remove the saucepan from the stove; let cool. Transfer to a bowl, cover, and refrigerate until needed.
