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How Does Water Quality Affect Water Supply?
 
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There is a clear relationship between water use and water quality. The amount and kind of minerals and organic substances in water affect its suitability for certain uses and greatly affect the type of treatment required to make it usable. For example, most rural homes must have water softeners because the water in three of every four wells contains iron in concentrations >0.3 milligrams, enough to cause staining. One of the many uses of rivers and streams has been the assimilation, dilution, and transport of water-borne wastes, which has made the water unsuitable for most purposes unless it is treated.

The quality of water varies regionally. For example, streamwater in northern Illinois is 15% harder than streamwaters in southern Illinois. Variations in the chemicals found in aquifers are quite large, with major differences between water quality of sand-and-gravel, sandstone, and limestone wells. Minerals in groundwater are contact-related and, therefore, a result of geology and residence time. Minerals in surface water are generally those of surface soils, although streams are influenced by groundwater that feeds surface flows. Other minerals are added by public, industrial, and agricultural uses of water.

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Municipal wastes are largely organic, but industrial wastes can include toxic metals, salt brines, strong acids and alkalies, dyes, and organic and inorganic chemicals. Agricultural wastes include fertilizers and pesticides, livestock wastes, plus sediment from erosion that reduces water storage capacity of lakes and reservoirs. Excessive pollution exists in some areas of Illinois, but it has not destroyed the resource. Areas of major problems have included streams and canals in the Chicago region and parts of the Illinois River. Varying degrees of stream pollution have been accepted because it has long been considered necessary for water courses to carry wastes. Water quality in Illinois has improved tremendously in recent years, and a major program to improve the Illinois River quality is ongoing.

Concentrations of natural chemicals, pollutants, and sediments in water can increase costs of making water available. Primary quality problems associated with waters in Illinois include turbidity, total dissolved minerals, mercury, iron, manganese, nitrate, hardness, methane, and pathogens. All of these can be treated, and cost is the controlling factor in the treatment levels chosen.

Community water treatment plants handle needs of local water supplies, and many of the state's treatment plants soften water. Treatment plants also exist at some industries. Common methods of treating water include sedimentation, filtration through sand, disinfection (usually with chlorine), aeration, softening, removal of iron and other minerals, the prevention or removal of undesirable tastes or odors, and addition of fluoride.

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Radium (Ra) in water from the deep bedrock aquifer system Radium (Ra) is prevalent in groundwater from the deep bedrock aquifer system of northern Illinois. The highlighted area shows where the combined Ra226 and Ra228 concentrations exceed the USEPA maximum contaminant level (MCL) of 5 picocuries per liter (pCi/L) in deep bedrock wells. (Source: Kay, 1999; http://il.water.usgs.gov/proj/
gwstudies/radium/
)
 

 
Water quality changes in shallow Kane County public water system wells This graph shows an alarming increasing trend in chloride in numerous shallow Kane County public water system wells. Chloride is a major constituent in road-salt used for deicing wintry roads. As more emphasis is placed on the development of shallow groundwater resources because of water availability concerns from other sources (the deep bedrock aquifers and Lake Michigan), it is important to protect these vulnerable aquifers.
 
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