Pour water and vinegar into a saucepan, and bring to a boil over high heat. Stir in sugar, ginger, garlic, chile pepper, and ketchup; simmer for 5 minutes.
In small bowl, mix a little bit of water with your cornstarch til there aren't any lumps. Then stir mixture into the saucepan.
Remove saucepan from stove to cool. Then transfer to a bowl or dressing bottle and refrigerate until needed.
