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Water Hardness

The City monitors the water hardness of its wells in order to help residents determine the proper settings for water softeners. Residents may check the specific level of hardness on the Water Hardness Map. The hardness levels indicated on this map are generalized according to the well with the hardest water servicing each area, which is a worst-case scenario. Exact water hardness may vary. Below is a detailed explanation of water hardness. Feel free to contact the Public Works Department at (630) 377-4405 or with questions or for additional information on water hardness.

More Information on Water Hardness

Hard water is a very common occurrence, affecting water in more than 85% of the country. Because more than 60% of the earth’s water is groundwater, it travels through rock and soil, picking up minerals, including calcium and magnesium, along the way. These minerals produce what is commonly referred to as “hardness” in water. Generally, hardness is measured in grains per gallon (gpg), parts per million (ppm), or milligrams per liter (mg/l).

1 gpg = 17.1 ppm
1 ppm = 1 mg/l

Almost all of Illinois has hard or very hard water, which means the water contains a high degree of the calcium and magnesium mineral ions. It is evident in homes as shown by crusty deposits around faucets, film on glasses, bathtub rings and sticky soap residue that is difficult to rinse out of clothes (some detergents include water softening agents to counteract hard water). Following is a chart that shows ranges of water hardness, as provided by the University of Illinois Extension Office.

Level of HardnessGrains per GallonParts per Million or mg/l
SoftBelow 1.0Below 17.1
Slightly Hard1.0 to 3.517.1 to 60
Moderately Hard3.5 to 7.561 to 120
Hard7.5 to 10.5121 to 180
Very Hard10.5 and above180 and above

The Environmental Protection Agency (EPA) establishes standards for drinking water that fall into two categories—Primary Standards and Secondary Standards. Primary Standards are based on health considerations, and Secondary Standards are based on aesthetics such as taste, odor, color or corrosivity. There is no Primary or Secondary standard for water hardness. In fact, the National Research Council (National Academy of Sciences) states that hard drinking water generally contributes a small amount toward total calcium and magnesium human dietary needs. In some cases, where dissolved calcium and magnesium are very high, water could be a major contributor of calcium and magnesium to the diet (National Research Council, Drinking Water and Health, Volume 3, National Academy Press, Washington, D.C., 1980).


Water Softening
Homeowners with Hard and Very Hard levels of hardness may consider softening their water with a central water conditioning system connected to the water lines. Packaged water conditioners can be used to soften water for bath or showering, but these add to laundering costs and are not as convenient.

There are many different types of softeners, each with its own benefits. An ion exchange softener, however, is the type most often used in homes. The water is softened when the hardness ions (magnesium and calcium) are exchanged for sodium ions. This exchange occurs in a resin bed during the softening cycle. The resin bed is made up of tiny bead-like material often made of styrene and divinylbenzene. The beads attract and hold positively charged ions such as sodium, but will exchange them whenever the bead encounters another positively charged ion, such as calcium or magnesium. A brine tank holds the dissolved salt solution that is necessary to regenerate the resin. Regeneration refers to reversing the ion exchange operation. The magnesium and calcium ions are driven off of the resin beads and replaced by positively charged sodium ions. The regeneration occurs when the resin beads are washed with a strong salt-water solution. The salt forces the calcium and magnesium ions to be released, and they are then discharged as waste during the backwashing cycle. The beads are then ready to attract hardness ions from the water again. Many installed softeners are fully automatic and regenerate according to a preset clock or water usage.

When purchasing a softener, be sure to take into consideration the number of people in the household, how much water is used, and the hardness of the water. The chart below will help you to choose a water softener size that is right for your needs. You will need to know the number of people in your household and the grains of hardness per gallon in your water.

Hardness in Grains per GallonNumber of People in Family +1*

This reference guide is based on every 4th night regeneration.
*Additional person compensates for water using appliances.

Iron Count
City water iron counts range from zero to .2ppm. These iron levels are not enough that the softener needs to be set to compensate. 

Formula for sizing softeners:

Capacity = No. of People x Hardness x 70 Gallons x Days Between Regeneration

Ex: A family has 4 people with 33 grains per gallon hardness with no iron.

4 + 1(for appliances) x 33 Grains/Gal. x 70 Gallons x 4 Days = 46,200 Grains. In this example, 46,200 grains of capacity is needed on average every 4 days. Because no iron is present, the low salt setting can be used. Select the softener that will provide more than 46,200 grains at the low salt setting.

A water softener will remove clear water iron (iron in solution). When removing iron with a softener, compensate the hardness by a factor of 5 grains per gallon for every part per million of iron.

Ex: A family has 3 people with 22 grains per gallon hardness and 3 parts per million iron.

3 + 1(for appliances) x 37 Grains/Gal. x 70 Gallons x 2 Days = 20,720 Grains. In this example, 20,720 grains of capacity is needed on average every 2 days. With iron present, the softener should regenerate every other night and use the medium salt setting. Select the softener that will provide more than 21,000 grains at the medium salt setting.

For some, the fact that sodium is used to soften water raises concerns about potential health risks. The health effect associated with a high intake of salt, though, are from sodium chloride, not sodium bicarbonate, which is the result of softening. Drinking water also represents a small portion of sodium intake in most people. Water softening systems using salt do not introduce enough salt to be of concern. These findings are confirmed by Dr. Andrew Zeifer, Director of the Hypertension Clinic at the University of Michigan, the New England Journal of Medicine, and the U. S. Environmental Protection Agency. Consumers on a strict, low sodium diet who are concerned about softened water may choose to connect their water softener to the hot water line only. Another option would be to install a reverse osmosis or distillation system.

updated Oct 15, 2018