Lower Illinois Regional Demands: Visualizing Water Use
How does water get used in the Lower Illinois Region?
The Illinois Water Inventory Program (IWIP) has been a core component of the Illinois State Water Survey (ISWS) since 1978. The Lower Illinois Region has five major water use sectors: public supply, domestic, industrial, agricultural, and environmental use (as seen in figure below).
Surface Water Demands
In the Lower Illinois Region, there are four major sources of surface water for water supply: the Illinois River, Mississippi River, regional tributaries, and inland reservoirs. The total surface water withdrawals in the Lower Illinois Region were approximately 14 million gallons per day (mgd) in 2020. At present, all reported surface water withdrawals are used by either the environmental or public supply sectors. Environmental demands occur in the southwestern counties along the Illinois and Mississippi Rivers while public supply demands occur predominantly in Macoupin County with intakes on reservoirs and tributaries.
Groundwater Demands
Aquifers are underground water sources that are naturally supplemented by rainfall, snowmelt, and other water that seeps into the soil. Many farmers use irrigation, which draws water from these groundwater aquifers. Reduced groundwater levels and, consequently, reduced crop yield potentially result from the aquifers' rapid depletion. Climate is a major driver of water use for agriculture with increased precipitation associated with decreased demands. The table below shows the relationship between annual precipitation and agricultural demands. For example, in the wet year 2015, water use for agriculture was approximately 5 mgd.
While some sectors consistently report to IWIP (public supply, industrial, environmental), other sectors have inconsistent reporting (agricultural) or are not required to report (domestic). Furthermore, these sectors often rely on different sources of water (e.g., groundwater, reservoirs, or streams) depending on their location in the region and the amount of water that they need to withdraw.
Estimated and IWIP reported values are shown in the figure below. Agriculture was estimated to be the largest water demand sector, followed by the public supply, and environmental sectors.
Funding Information
This story map is part of a series about Water Supply Planning throughout the state of Illinois. Water Supply Planning is an ongoing research effort conducted by the Illinois State Water Survey and is funded by the Illinois Department of Natural Resources Office of Water Resources.