Illinois Water Supply Planning



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Surface Water Sources and Public Water Supply IntakesBack
 
Community water supplies provide nearly 90 percent of Illinois' citizens with water for residential use. The Illinois Environmental Protection Agency (IEPA) defines a "community water supply" as a public water supply that provides potable water to a minimum of 15 service connections used by year-round residents or regularly serves at least 25 year-round residents. The IEPA issues permits for operation of water supplies serving the public. Water withdrawal data are collected by the Illinois State Water Survey (ISWS) through the Illinois Water Inventory Program (IWIP).

Water withdrawals of surface water and groundwater by community water supplies in Illinois exceeded an average rate of 1700 million gallons per day (mgd) in 2000. Of this total, 64 percent was withdrawn from Lake Michigan; (http://il.water.usgs.gov/proj/lmda/), 17 percent from rivers, streams, and reservoirs, and 19 percent from groundwater sources. Surface water was the source of nearly 1400 mgd provided by community water supplies.

The IWIP was initiated in 1978 to centralize Illinois’ diverse array of water quantity information. State agencies and other professionals use IWIP data for research and studies involving water withdrawals, water use, and water returns. The Public-Industrial-Commercial-Survey (PICS) database, developed and maintained at the ISWS for the IWIP, contains site-specific information for 10,504 active and inactive high-capacity withdrawal point sources from 4,248 facilities throughout Illinois. The PICS database covers public water supply wells and surface water intakes, high-capacity private wells that generate more than 70 gallons per minute, and surface water intakes for industry, commercial establishments, and fish and wildlife management areas. The PICS database also contains detailed annual pumpage information for wells and surface water intakes since 1978. Water use data from this database are included in the U.S. Geological Survey's National Water Use Data System, and that agency and the ISWS periodically publish reports on water withdrawals.

Many communities in central and southern Illinois depend on surface water from relatively small streams and rivers that have periods of extremely low flow. Most systems depend on some form of raw water storage, either impounding or off-channel reservoirs. An impounding reservoir is created by a structure built across a natural stream or river. An off-channel (or side-channel) reservoir is filled primarily with water from a source other than natural surface runoff. Water is pumped from the raw water source (reservoir, lake, stream, or river) to the off-channel reservoir for storage.

Many community supply systems have multiple surface water sources: two or more impounding reservoirs, an impounding reservoir and an off-channel reservoir, or multiple river intakes at different depths. Pumping installations in reservoirs and rivers are typically called intakes. Total withdrawals from six Lake Michigan intakes serving the Chicago area exceeded an average of 100 mgd per intake in 2000. Withdrawals at all other surface water intakes were below 50 mgd in 2000. If water withdrawals are not metered at individual locations, total raw water withdrawn by the community supply is allocated equally among various active intakes.

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Illinois Community Surface Water Supplies
The map of community surface water resources shows active surface water intakes in 2000, but communities occasionally change sources of supply for a variety of reasons. Intake locations are shown and markers indicate relative magnitude of water withdrawal in 2000 from PICS data.

Monitoring of water withdrawals by community water supplies provides essential information about the historical and current use of Illinois' water resources and assists with planning and decision making. The demand for water is increasing, and it is vital to assess water withdrawals, demands, and use to help ensure a reliable supply of clean water into the future.


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Illinois State Water Survey

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