This guide is intended to help citizens of Illinois find information about Illinois water supplies.  It includes information resources from the state and federal government, news sources, and library holdings (including digital collections). 

Water supply for Illinois comes from a variety of sources including surface waters (i.e., rivers, lakes, reservoirs), groundwater from aquifers of various types, and private shallow wells.  Use of water in Illinois includes residential (both municipal supplies and private wells), agricultural (irrigation and livestock), commercial, and industrial purposes.  

A public water supply is defined as "all mains, pipes and structures through which water is obtained and distributed to the public, including wells and well structures, intakes and cribs, pumping stations, treatment plants, reservoirs, storage tanks and appurtenances, collectively or severally, actually used or intended for use for the purpose of furnishing water for drinking or general domestic use and which serve at least 15 service connections or which regularly serve at least 25 persons at least 60 days per year." A community water supply is a public water supply that serves or is intended to serve at least 15 service connections used by residents or regularly serves at least 25 residents. A non-community water supply is a public water supply that is not a community water supply. 

More info:

Illinois Water Supply - Information on Illinois Water Supply from the  the Illinois State Water Survey

Public Water Supply - Information on legislation and programs of the Illinois Environmental Protection Agency.