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 Of this total, 64 percent was withdrawn from Lake Michigan; (http://il.water.usgs.gov/proj/lmda/),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.
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.
|Illinois Community Surface Water Supplies|
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.