Recurring Supply and Demand Challenges in Water Supply Planning Studies
The Illinois State Water Survey (ISWS), in partnership with the Illinois Department of Natural Resources (IDNR), is completing water sustainability analyses of each water supply planning region (WSPR) of Illinois. While the state is home to 10 distinctive WSPRs and one sub-region, common issues emerge across the state.
This summary of recurring water supply challenges is based on completed studies in the state: East Central IL (2011), Kaskaskia Region (2012), Northeast Illinois (2012), Middle Illinois (2018), Kankakee (2019), Rock River (2023), Lower Illinois (2023), American Bottoms (2024), and Big Muddy (in development).
Unexpected Demands
At its core, water supply planning efforts analyze the balance of available supply versus current and projected demand. Unexpected demands offset the sustainable balance of a region’s water supply. Throughout the different regions of Illinois, these new or unexpected demands will take different forms. The most recurring reason for new demand is population growth. In the Kaskaskia River WSPR, the authors highlighted that future reservoir supply may be insufficient to meet community growth projections. New industries also can significantly reduce supply. In northeast Illinois, communities’ reliance on the confined sandstone aquifer system become threatened with the installation of a data center. In the Lower Illinois region, environmental uses of water, such as creating habitat for waterfowl, can be an unexpected demand on water supply.
Drought
Through drought, water supply available in surface water and groundwater is reduced. Drought can devastate agricultural areas such as the Rock River WSPR. Extreme drought can also lead to low or no streamflow conditions as observed in many water supply planning regions. Community water supply can also be threatened by drought. In East Central WSPR there is an estimated 50% probability that Bloomington and Decatur would not be able to meet community supply demands if the worst drought on record were to happen again.
Flooding
As Illinois’ climate becomes wetter, flash flooding is projected to become more of a common occurrence. In the American Bottoms WSPR, an area dominated by the flood stage of the Mississippi River, pumping is needed to maintain non flooded conditions along roadways and neighborhoods. In the Big Muddy WSPR, stakeholders have discussed with the water supply planning team that mitigating flooding risk is more of a priority than drought preparedness.
Aging Infrastructure
As water supply infrastructure ages, communities can see diminished returns for their initial investment. Maintenance of reservoirs (through bathymetric surveys) and wells (through rehabilitation) are necessary to keep water supply infrastructure operating efficiently. Wells in the American Bottoms WSPR need regular rehabilitation because of mineral scaling issues. The Big Muddy WSPR is currently draining a lake that was contained by a dam no longer robust enough for peak flood conditions.
Water Quality
While water quality issues in surface and groundwater are diverse throughout the WSPRs, common issues emerge. Arsenic concentrations exceeding the US Environmental Protection Agency primary standard are naturally occurring in aquifers throughout the state. Chloride concentrations elevated beyond the US Environmental Protection Agency secondary standard are more prevalent in waters near Chicago but can be high in rivers and aquifers elsewhere in the state. Elevated nitrate from agricultural practices have been observed in agricultural areas throughout the state. Iron and other metals can be elevated and lead to scaling issues in infrastructure.
Illinois Water Supply Planning Regions
