|What are the Dimensions of Water Availability in Illinois?
Illinois is a water-rich state with resources adequate to meet most existing and future
demands for water. However, in areas with high population growth future demands may
well exceed existing available water resources.
In areas of rapid and extensive growth there is a competition for water to meet demands. These include off-stream uses of water such as
public supplies, industry, commercial concerns, power generation, agriculture, and irrigation, as well as in-stream
uses such as navigation, wildlife, aquatic habitats, and waste dilution. Furthermore, drought can temporarily reduce
water supplies in any area, creating competition for a limited resource.
Where does our water come from? The water cycle depicts water moving through the atmosphere and on and under the surface of the earth.
Another term for the water cycle is hydrologic cycle. Water moves:
downward as precipitation, into the soil and through the unsaturated zone as infiltration, and through
the saturated zone to shallow and deep aquifers as recharge; laterally on the surface as surface runoff to lakes, wetlands, streams, and rivers and underground as groundwater flow;
upward as evapotranspiration from lakes, wetlands, streams, and rivers, plants, soil, and groundwater, and as
groundwater discharge to surface waters; and
laterally aloft as atmospheric moisture, where condensation forms clouds.
Arrows depict movements in the water (hydrologic) cycle.
Groundwater comes from wells that
tap into aquifers at varying depths. Owing to Illinois' geology, the northern third of the state has several high-yielding
aquifers and most communities there rely upon groundwater. These aquifers include numerous sand-and-gravel aquifers above the bedrock surface,
shallow bedrock dolomite and limestone aquifers (less than 300 feet deep), and deep bedrock
limestone and sandstone aquifers (>300 feet deep). Water quantity and its quality varies greatly
among aquifers. (See More Information for maps of these aquifers.)
Farms and rural residents all across Illinois rely on private shallow wells for their water
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This graphic depicts Illinois' major freshwater sources as a series of stacked overlay maps. Layers include average annual precipitation (in inches, top map), major rivers and their watersheds (middle) and major aquifers (bottom). This depiction demonstrates the regional variability of Illinois' water resources and that the boundaries of watersheds and aquifers do not coincide. Nor do they coincide with political boundaries. Solutions to regional water supply issues must recognize the differing scales of watersheds and aquifers.
This image shows the different water supplies that Illinois utilizes. Again, it helps illustrate that Illinois' water sources vary by region across the
state. A map of Illinois is provided, with rough locations of surface water intakes (public water supply), sand/gravel aquifers, and some bedrock aquifers.
Source for aquifer boundaries, Illinois State Geological Survey
Surface water supplies are displayed in this graphic. The different supplies are spread throughout Illinois.
These surface water supplies include lakes, reservoirs, rivers, and streams.