Illinois Water Supply Planning



Water Availability

Where does our water come from? The main sources of water in Illinois are the primary factors in the water cycle, including precipitation, surface water, and groundwater. Water moves downward as precipitation; becomes groundwater by moving into the soil and through the unsaturated zone as infiltration and through the saturated zone to shallow and deep aquifers as recharge; and on the surface as runoff to lakes, wetlands, streams, and rivers.

It also moves upward as evapotranspiration from lakes, wetlands, streams, rivers, plants, and soil, and laterally as groundwater discharge to surface waters; and laterally aloft as atmospheric moisture, where condensation forms clouds. Drought also temporarily reduces water supplies, creating competition for a limited resource. Climate change could alter the availability of water for decades or permanently.

Illinois is a water-rich state, but water availability and demand vary widely across the State. A large portion of the population in northeastern Illinois uses surface water from Lake Michigan, although this source is limited by court order because the water is diverted. Surface water from rivers and reservoirs provides water throughout Illinois. Many communities in the northern third of Illinois rely upon groundwater from several high-yielding aquifers including sand-and-gravel aquifers above the bedrock surface, shallow bedrock dolomite and limestone aquifers, and deep bedrock limestone and sandstone aquifers. The high-yielding Mahomet Aquifer supplies groundwater in east central Illinois. Residents in rural and unincorporated areas all across Illinois rely on private shallow wells for their water supply.

Water Cycle


Potential Impacts of Climate Change on Water Availability (pdf ~800kb)

Water Supply Planning and Management: Climate Variability and Change (pdf ~1.5mb): Presented by Derek Winstanley, Chief, Illinois State Water Survey, on June 29, 2007 at a meeting of the East Central Illinois Regional Water Supply Planning Committee in Decatur, Illinois.

Surface Water


The Significance of an Observation Well Network in McHenry County (pdf ~8.6mb): A 4/16/08 presentation to the McHenry County Groundwater Protection Task Force.

Groundwater Surface Water Interactions

Groundwater Recharge in Northeastern Illinois (pdf ~2.4mb): A 4/22/08 presentation to the Northeastern Illinois Regional Water Supply Planning Group.

U.S. Geological Survey Circular 1139, Ground Water and Surface Water A Single Resource: Many natural processes and human activities affect the interactions of groundwater and surface water. This report presents an understanding of these processes and activities as well as limitations in that knowledge.

Illinois State Water Survey

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Champaign, IL 61820-7463

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