Dishwasher - Detergent Use and Water Hardness

Using the right amount of liquid or powdered detergent is important if you are 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 from your dishwasher.


What is hard water?

  • Water that is "hard" has a high level of dissolved minerals such as calcium and magnesium. As the concentration of the dissolved minerals increases, the water becomes harder.

  • Water hardness is measured in grains of hardness per gallon of water (grains per gallon). Your Water Utility Company or County Extension Agent can tell you how hard the water is in your area. Just call and ask how many grains of hardness 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/pre-wash cup of detergent to achieve a good wash performance.

  • Soft water: Very soft water only requires a 1/3 cup of detergent in the main cup for good wash performance.

  • In Between: Anything in between will require judgment. Use enough detergent 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.


Listed below is a general guide on the amount of detergent recommended based upon your water hardness (grains per gallon):

Soft Water (0-3 grains):

  • Fill the main wash cup to 1/3 full.

Medium Water (4-8 grains):

  • Fill the main wash cup to 2/3 full.

Hard Water (9-12 grains):

  • Fill the main wash cup completely full.

Very Hard Water (Over 12 grains):

  • Fill both the main wash cup and the pre-wash cup completely.