How much detergent should I use based on my water hardness?

The amount of detergent depends on how soiled the items are and the hardness of your water — heavily soiled loads and harder water require more detergent. For soft to medium water (0–6 grains per U.S. gallon), use less detergent; for medium to hard water (7–12 grains per U.S. gallon), fill the Main Wash section to the higher level shown. Using too little detergent in hard water will result in unclean dishes, while using too much in soft water can cause glassware to etch. (Page 4)