Dishwasher Detergent Use and Water Hardness

Using the right amount of liquid or powdered detergent is important if you're not using a detergent pod, tablet, or packet. Soft water requires less detergent, since too much detergent can cause etching of glassware. Hard water requires more detergent to get good wash performance.

What is Hard Water?

  • Water that is "hard" is high in dissolved minerals, like calcium and magnesium. As the concentration of the dissolved minerals increase, the water becomes harder.
  • Water hardness is measured in grains of hardness per gallon of water (grains per gallon). Your Water Department or County Extension Agent can tell you how hard your water is. Just call and ask how many grains of hardness (impurity) there are in the water.

How much detergent do I use?

  • Hard water: Very hard water requires a full main cup and a full open cup to get good wash performance.
  • Soft water: Would only need a half full detergent cup.
  • In Between: Anything in between will require judgment. Use enough to get the job done, but don't use more than you need. As a rule of thumb: Harder water requires more detergent; softer water requires less detergent.

 

Amount of detergent recommended (general guide):

Soft Water (0-3 grains)

  • Normal Wash: Main cup/half full; Open cup/empty
  • Short Wash: Main cup/half full; Open cup/empty


Medium Water (3-7 grains)

  • Normal Wash: Main cup/completely full; Open cup/half full
  • Short Wash: Main cup/half full; Open cup/empty


Hard Water (7-12 grains)

  • Normal wash: Main cup/completely full; Open cup/completely full
  • Short Wash: Main cup/completely full; Open cup/empty


Note: Anything over 12 grains is extremely hard water and a water softener is recommended.