Illinois Water Inventory Program: A Data Foundation for Local Water Supply Planning

Reliable water-use information is essential for water supply planning. The Illinois Water Inventory Program (IWIP) serves as a central source of water-use information and water research data in Illinois. In turn, those data provide an important foundation for regional and local water supply decisions and long-term water supply planning across the state.
​
What is the Illinois Water Inventory Program (IWIP)?
​The Illinois State Water Survey’s Illinois Water Inventory Program (IWIP) began in the late 1970s as a repository for the Illinois’ water-use data. Initially a voluntary, mail-based reporting system, reporting became mandatory after a 2010 amendment to the Illinois Water Use Act of 1983 (Public Act 096-0222) , reflecting the state’s need for more complete and consistent water-use data to support planning and research. Despite this need, there are no penalties for failing to report water withdrawals to IWIP, and the program lacks a dedicated funding authorization. At the time of this writing, IWIP was funded primarily through annual state appropriations administered through the Illinois Department of Natural Resources (IDNR), meaning its continued operation depends on annual budget decisions and is not automatically guaranteed.

​How does IWIP reporting work?
IWIP collects annual water-use data across several sectors, including: public water suppliers (PWS); self-supplied industry (SSI) with high-capacity wells or intakes rated at 70 gallons per minute or more; and agricultural irrigation users, particularly high-capacity center-pivot systems. In 2014, the program moved to an online reporting system, reducing manual data entry and improving the processing of water-use records. The program includes records from about 5,770 facilities, more than 3,200 of which are active and receive notification from IWIP of their obligation to report annual water withdrawals.
 
Before water withdrawals are reported through IWIP, the well or intake has already been permitted and constructed under Illinois law and applicable rules. IWIP data collection begins when those withdrawals are registered. This registration is not a permit process; instead, it allows ISWS to identify new withdrawals, link wells to construction records where relevant, assign facility and point IDs, and establish annual online reporting.
 
What kind of data does IWIP collect?
The information submitted through the ISWS Online Reporting Tool varies by facility type and includes both point-level and facility-level data. Point-level data include individual withdrawal points and include information such as annual gallons pumped and water levels. Facility-level data capture the location and amount of water withdrawn at each of the multiple points associated with the facility, , as well as broader water-use information, including water use by category and any water purchases or sales. IWIP supports data quality through data review, standardized reporting, and operator tools that allow users to review historic reports and maps of listed wells and intakes, improving reporting accuracy.
 
How are IWIP data used?
IWIP data support a range of water planning and research efforts in Illinois, including groundwater flow modeling, surface water hydrology studies, state water supply planning, regional aquifer studies, municipal projects, consultant analyses, and more. IWIP data have also been used in externally funded efforts including the U.S. Army Corps of Engineers’ Lake Michigan Diversion Accounting Program, the Illinois EPA’s Source Water Assessment Program website, the U.S. Geological Survey’s National Water Use Information Program estimates series, CMAP’s Regional Demand Forecast, and the Upper Mississippi River Basin Association’s Cumulative Impacts Assessment. At the local and regional level, IWIP data have informed water planning in Kendall, McHenry, and Kane County, including Kane County shallow groundwater sampling, as well as broader initiatives such as the Northwest Water Planning Alliance Water Supply Sustainability Plan and Northeastern Illinois.
 
How can IWIP data and tools be accessed?
IWIP data can be accessed through interactive online maps and tools, IWIP Water Use Reports, and custom data requests. Publicly available information includes well and intake records, public water supply water withdrawals and water level information, aggregate self-supplied pumpage data by county or watershed, and more. Several online tools make IWIP data easier to explore and use, for example the Illinois Water Budget Vista (IWBV), the Community Water Supply Wells Map, the Public Water Supply Reporting Map, the Center Pivot Irrigation Map and the Statewide Municipal Water Use and Water Purchase Map. IWIP data are also organized by USGS water use categories to ensure integration with national datasets. For custom data requests, users can contact the IWIP Coordinator, Cora Wessman, describe the data needed and the purpose of the request, discuss the project, sign a data license agreement, and then receive the data.
 
Conclusion
​The Illinois Water Inventory Program provides critical information for water resource management, planning, and research across Illinois. By maintaining a consistent statewide record of water withdrawals, IWIP supports understanding of water-use and provides a foundation for long-term water supply planning, The program, however, faces ongoing challenges, including lagged data availability, low and inaccurate reporting in the agricultural water-use sector, and reliance on annual appropriations rather than a dedicated funding source. Continued improvements in the funding, timeliness, completeness, and accessibility of IWIP data would further strengthen its value for utilities, planners, researchers, and policymakers.