Commonly Found
Substances in
Drinking Water
And
Available
Treatment
Illinois Department of Public Health
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Introduction
This pamphlet discusses common constituents – hardness, sulfates, iron,
chlorides, pH (acidity and alkalinity), total dissolved solids and hydro-
gen sulfide – of drinking water. Separate pamphlets on lead, nitrate,
bacteria and parasites in drinking water are available from the –
Illinois Department of Public Health
Division of Environmental Health
525 W. Jefferson St.
Springfield, IL 62761
217-782-5830
TTY (hearing impaired use only) 800-547-0466
Hardness
The hardness of water is a measure of the amount of minerals, primarily
calcium and magnesium, it contains. Water softening, which removes
these minerals from the water, may be desirable if –
• Large quantities of detergent are needed to produce a lather when
doing laundry, or
• Scale is present on the interior of piping or water tanks, laundry
sinks or cooking utensils.
Water that contains more than 200 mg/l (milligrams/liter) or 200 ppm
(parts per million) as calcium carbonate (CaCo3), or 12 grains per gal-
lon, is considered to be hard and may cause plumbing and laundry stain-
ing problems. (Three grains per gallon equals approximately 50 ppm.)
Methods used to soften hard water for home use are zeolite softening
and reverse osmosis.
The following is a measure of hardness (expressed in mg/l as CaCo3):
0 - 100
Soft
100 - 200 Moderate
200 - 300 Hard
300 - 500 Very hard
500 - 1,000
Extremely hard
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Zeolite softening (ion exchange) depends on the ability of granular
materials, called zeolites, to exchange ions present in their structure for
ions present in the water. As the hard water percolates through the zeo-
lite bed, the calcium and magnesium ions in the water are exchanged for
sodium ions in the bed, making the water soft. The calcium and magne-
sium ions are left attached to the zeolite grains. Wh