Water Hardness


Hard water is not a health hazard.  The United States Environmental Protection Agency (USEPA) establishes standards for drinking water, Primary Standards – based on health considerations, and Secondary Standards – based on the aesthetic properties of water.  There is no Primary or Secondary Standard for water hardness.

Calcium and Magnesium dissolved in water are the two most common minerals that make water “hard.”   Water hardness is expressed as the amount of Calcium Carbonate (CaCO3) measured in the water and can be communicated using any one of the following units:

  • milligrams per liter (mg/L)
  • parts per million (ppm)
  • grains per gallon (gpg)

One grain per gallon of hardness equals 17.1 mg/L or ppm of hardness.  (Note: mg/L = ppm)

Classification of Water Hardness (United States Geologic Survey, USGS)
 Classification  Milligrams per liter (mg/L) or parts per million (ppm) Grains per gallon (gpg)
 Soft  0 - 60  0 - 3.5
 Moderately  Hard  61 - 120  3.5 - 7.0
 Hard  121 - 180  7.0 - 10.5
 Very Hard  Over 180  Over 10.5


Soquel Creek Water District’s water hardness is classified as hard to very hard.  If you choose to utilize a water softener, the USEPA recommends* the selection of a device that is certified by one of the following three organizations, which are accredited by the American National Standards Institute (ANSI):

*Recommendations included in USEPA’s Home Drinking Water Filtration Fact Sheet HERE.

Frequently Asked Questions about Hard Water

Q:  What is hard water and what can I do about it?

Hard water is simply water that contains two harmless minerals - calcium and magnesium.  Water is considered "hard" if it measures more than 120 parts per million or 7.0 grains per gallon.

Although hardness does not affect the safety of the water, some customers may find it to be inconvenient. The minerals may make the water hard to develop a sudsy lather. Hardness minerals may also contribute to scaling in teapots, spots on dishes and residues on plumbing fixtures and glass shower doors.

Q: We recently purchased a new dishwasher. In order to establish the correct settings, the dishwasher requires us to program the level of hardness/softness of the water. What is the water hardness in the grains per gallon (gpg)?

In Capitola/Soquel area, the range of water hardness is about is 140-360 parts per million (ppm) or 8.5 to 21 grains per gallon (gpg).

In Aptos/Rio del Mar/La Selva Beach area, the range of water hardness is about 75-240 ppm or 5 to 14 gpg.

Q: My showerhead and shower doors have a white film on them. What causes it and what should I do about it?

The white film is the residue of hardness and other minerals in the water. When the water is heated or evaporates, the minerals leave a white coating on items such as showerheads, shower doors, glasses, coffee pots, etc.

Although harmless, most people don't appreciate a white film on these household items. Many customers install a water softener unit.  In terms of cleaning hard water spots, there are several cleaning products on the market made specifically for its removal. A "green" alternative is warm vinegar. Soaking in vinegar can help dissolve the spots. Make sure you rinse the items carefully after the vinegar "bath" before using them. This method is less practical for shower doors. In the case of shower doors, prevention is the best medicine. Wipe down the doors with a sponge or towel after every shower.