What is Hardness?

Hardness is a measure of the concentration of calcium and magnesium in the water. Because groundwater is in contact with rocks and minerals, it absorbs those minerals, causing groundwater supplies to have more hardness than most surface waters, which come from lakes and streams fed by rainwater.

The hardness of the water causes no health problems, and is a source of calcium and magnesium in the diet. However, calcium in the water is deposited on dishware and other surfaces, causing spots. The City imports State Water, which is lower in hardness than the local supply, to provide a water supply that has a lower hardness. In the water industry, hardness is usually discussed in units of milligrams per liter (mg/L); however, water softener manufactures usually refer to hardness in units of grains per gallon (gpg). One grain per gallon is equivalent to 17.1 milligrams per liter. The table below shows the hardness of various local water sources.

Water Source	Hardness (mg/L)	Hardness (gpg)
State Water	120 mg/L	7 gpg
Typical Blend	250 mg/L	15 gpg
Maximum Blend	300 mg/L	18 gpg
Minimum Local Groundwater	420 mg/L	25 gpg
Maximum Local Groundwater	730 mg/L	43 gpg

Some people prefer their water to be softer than what the City is able to provide. If you are considering purchasing or replacing a softener, please consider softeners that use exchange tanks instead of self-regenerating softeners. Dumping a bag of salt in a self-regenerating softener is equivalent to dumping that same bag of salt directly into the local groundwater. Exchange tanks, which get regenerated offsite with the salt disposal outside our groundwater basin, are much more protective of our local groundwater supply.

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