1. Combine soy sauce, dry mustard, brown sugar, butter and water in a saucepan. Heat over medium heat, stirring often, until smooth. Let cool.
2. Place chicken legs in shallow glass baking dish, then pour sauce over legs.
3. Cover and refrigerate for 2 hours.
4. Bake for 1 hour at 350 F., turning legs over halfway through cooking.
Making your own Teriyaki will allow you to adjust the flavor, including the salt, to just the way you like it. You can, of course, make a batch of the Teriyaki to store in your refrigerator for other dishes, as well.