|How Does Water Quality Affect Water Supply?
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.
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