From The Changing Illinois Environment: Critical Trends, Volume 2: Water Resources , Technical Report of the Critical Trends Assessment Project


Illinois is fortunate that large quantities of both surface and ground water exist within the state, and these water resources have fostered population and industrial growth throughout the state's history. But the quantity of the available resources is limited. Some of the major metropolitan centers, such as the Chicago area, Peoria, Decatur, and Bloomington-Normal, have required the use of both surface and ground water to meet their needs for urban and industrial development and to sustain growth. The regular study of these water resources helps our understanding, and provides the factual basis for management strategies that could avert trends potentially detrimental to the availability of these resources. Monitoring also allows us to recognize the number of facilities and/or individuals dependent upon either surface or ground water that could be impacted by a variety of environmental or human-induced factors.


The majority of water use in Illinois falls within three categories: public water supply, self-supplied industry, and hydro and thermoelectric power generation. In 1991, combined surface water and groundwater withdrawals in Illinois totaled 20,637 million gallons per day (mgd), of which 1,886 mgd was for public water supplies, 614 mgd was for large self- supplied industries, and 18,136 mgd was for power generation. Thus, power generation is by far the leading water use in the state. Separate surface water and groundwater withdrawals were 19,448 and 1,189 mgd, respectively. Excluding power generation, surface and groundwater withdrawals totaled 1,887 and 614 mgd, respectively. Surface and groundwater withdrawals for public water supply were 1,429 and 444 mgd, respectively.

Most types of use return water to nearby streams after being used, regardless of the withdrawal source. In most cases the stream that receives the return flow is in the same major watershed as the point of withdrawal. Two major cases involve an interbasin transfer of water: 1) withdrawals from Lake Michigan are discharged into the Illinois Waterway; and 2) water used for the city of Bloomington is withdrawn from reservoirs in the Mackinaw River basin, but is discharged to the Sangamon River basin. A large percentage of the use is also basically nonconsumptive, meaning that the amount of water returned to streams is virtually the same amount that was withdrawn. Consumptive uses of water include that withdrawn for irrigation and the use of public water supply for watering lawns and gardens.

Table 1 compares 1991 Illinois water use with that for 1965, as given in Water for Illinois: A Plan for Action (ITACWR, 1967). This table indicates that the total water use in the state has risen by 27 percent in 26 years. Self-supplied industry has decreased, while water use for power generation has increased significantly. Public water supply (PWS) use has increased approximately 7 percent, which is less than the population growth (13 percent) during that time. The modest growth in PWS use can be attributed to water conservation, particularly from industrial and commercial users, and some leveling off in residential demand.

Kirk et al. (1979, 1982, 1984, 1985) and Kirk (1987) summarized surface and groundwater withdrawals in Illinois after sending an annual questionnaire to more than 4,000 PWS facilities and self-supplied industries since 1978. The Illinois Water Inventory Program (IWIP) was established to detail water use in Illinois in cooperation with the U.S. Geological Survey. Currently this program is fully funded by the Illinois State Water Survey and is the only statewide collection of these data on a regular basis. The program collects point-source water-use information and groups it within several categories. Collecting these data at the "point- source" level allows its aggregation into any number of environmental or economic categories. Several water-use investigations, including Water Survey Contract Reports 442 (Singh et al., 1988) and 477 (Broeren and Singh, 1989), employ the IWIP data. Water-use information for selected years between 1900 to 1978 has periodically been reported for individual facilities in unpublished memoranda at the Illinois State Water Survey. Many studies have been developed over the history of the Water Survey that contain water- use information compiled from these data. Two studies used herein are Water Survey Bulletins 21 (Habermeyer, 1925) and 40 (Hanson, 1950).

Trends in PWS Use and Number of Facilities

Table 2 indicates the number of surface and groundwater withdrawal facilities reported during the last 70 years in Illinois. The numbers listed are for supply sources and do not count water supply systems that obtain either raw or finished water from another system. The number of PWS facilities reported has almost tripled, increasing from 497 in 1925 to 1,442 in 1991. Much of the change in the number of facilities results from new water supply practices, consolidation of facilities, organization of individual users into water districts, and to a greater extent, a change in the criteria used to define a PWS. Currently, any facility that serves 25 individuals or 15 properties for 60 days or more in one year is considered a PWS. Development of new surface water sources, such as a major reservoir, can lead to a net reduction in the number of PWS facilities through consolidation. For example, more than 25 communities joined together to form the Rend Lake Conservancy District when that reservoir was built.

To present annual pumpage in this report, only PWS withdrawals >1 mgd were examined. These 162 facilities are the ones most at risk in regard to quantity and quality impacts because of their service to a significant number of people. Figure 1 shows the growth in total water use for these 162 facilities since 1961. The water-use data for individual years show greater fluctuation since 1980, a result of the more complete, detailed records that have been kept since the inception of the Illinois Water Inventory Program. Prior to 1965, much of the increased water use was associated with growth in per-capita consumption. Increases in water use since 1965 are more related to population growth, since the statewide consumption rate has changed only slightly during that time, remaining near 200 gallons per capita per day (gcd). This 200-gcd rate includes water for commercial uses and industry served by public water supplies. Strictly residential water use is approximately 80 gcd.

During drought years, the overall consumption rate may increase. For example, figure 1 shows a 10 percent increase in overall water use in the drought year of 1988. Figure 2 provides examples of the growth experienced since 1911 for three individual facilities: Bloomington, Elgin, and Dixon. Like most facilities in the state, these show consistent growth in water use since the 1940s.


The use of ground water for PWS is usually a preferred option for two reasons: 1) surface water must be treated to a greater degree, primarily for removal of bacteria and reduction in turbidity, and 2) unless a community is located near a river with sustained flow, then surface water storage (usually an impounding reservoir) must be created, which requires significant capital expenditure. Nevertheless, in terms of volume, surface water accounts for more than 75 percent of the PWS use in Illinois, and approximately two-thirds of the total population's domestic supply. Surface water supply systems have been developed in cases where the sustainable yield of the available groundwater resources is inadequate to serve the needs of the community. Conjunctive use of surface and groundwater resources is also becoming an increasingly viable option when a community outgrows the yield of their original source of supply.

Sources of Surface Water Supply

For the purposes of this project, four surface water supply sources were defined: 1) Lake Michigan, 2) border rivers, 3) intrastate rivers with sustained flow, and 4) reservoirs (both impounding reservoirs and side-channel reservoirs). Table 3 lists the approximate number of facilities by category for four separate years: 1930, 1954, 1970, and 1992. It is not unusual for the number of facilities in each category to differ from one year to the next, given typical changes in water supply practices. Figure 3 lists the change in overall use from 1961 to 1991 for each of these categories. With the exception of Lake Michigan and the border rivers, most surface water supply systems are located in the southern half of Illinois, where groundwater yields are particularly low. Figure 4 shows the location of all surface water withdrawals used for PWS. Lake Michigan. The lake is the source for approximately 1.1 billion gallons per day--more than half of the total PWS in Illinois and 75 percent of the portion coming from surface water sources. Since 1985 Lake Michigan water has been reallocated to many communities in DuPage and Cook Counties, which had previously obtained their water supply from the Cambrian-Ordovician aquifer system. These communities do not directly withdraw water from the lake, and therefore are not counted as additional water supply facilities in table 3. Water use from Lake Michigan is part of the total diversion allocated to Illinois from Lake Michigan, and as a budgeted amount, it is not likely to increase significantly.

Border Rivers. Direct withdrawals from border rivers (the Mississippi, Ohio, and Wabash) account for an additional 4 percent of the PWS use from surface waters. Much of the use from border rivers is concentrated in the metropolitan areas of East St. Louis and Rock Island-Moline.

Direct Withdrawals from Streams. Most of the streams and rivers in Illinois with the greatest sustained flow are in northern Illinois. These include the Rock, Kankakee, Fox, Pecatonica, Kishwaukee, and Illinois Rivers. For the most part, their water supply potential has remained untapped, primarily because the same region has abundant groundwater resources. In recent years, two large communities on the Fox River, Elgin and Aurora, have outgrown the availability of high- quality ground water and now obtain most of their water supply from the Fox. The city of Joliet has also mined its groundwater sources and is now evaluating the Kankakee River as a source. The Illinois American Water Company-Peoria, which serves the city of Peoria, now obtains almost 50 percent of its water from the Illinois River. Large rivers in the southern part of the state, specifically the Kaskaskia, Little Wabash, and Big Muddy, have also served as water supply sources for nearby communities.

Reservoirs. Prior to 1920, surface water supplies in the state were few, and most of these were direct withdrawals from streams. These systems' inability to meet increasing water uses started a boom in the construction of water supply reservoirs that continued through the 1930s. The number of new reservoirs constructed during this period is illustrated in figure 5. A second peak in reservoir construction occurred in the 1960s. In many cases, newer reservoirs were built to replace or serve jointly with old reservoir systems that had inadequate storage. The continued construction of reservoirs for water supply came to a halt in the early 1970s, primarily because of environmental concerns and large construction costs associated with reservoir construction.

Table 3 indicates the reduction in the number of water supply reservoirs since 1970. Much of this decrease results from the creation of the Rend Lake Intercities Water System, which serves 12 communities that previously had obtained water from their own reservoirs.

The growth in water use from reservoirs has increased more than 40 percent since the early 1970s, as shown in figure 2. However, during that same period of time no new impounding reservoirs have been constructed for water supply purposes, and only a few side-channel reservoir systems have been constructed. This means that greater demands are being placed on the existing reservoirs. Broeren and Singh (1989) indicate that 25 of these reservoir systems may not be sufficient to supply near-future water demands during a 50-year drought. Presently more than 11 percent of public water supply from surface waters comes from reservoirs, making it the largest source category other than Lake Michigan.

Trends in Surface Water Use

Per-capita use for PWS has not changed appreciably in the last 25 years, remaining near 200 gallons per day per capita (as estimated from present IWIP data and ITACWR, 1967). Future increases are therefore likely to be associated with population increase. Singh et al. (1988) estimated future water use based on population projections for 90 PWS systems using reservoirs and intrastate rivers as their primary supply source. The values from this study indicate that water use for most of Illinois is likely to increase 10 percent by the year 2020. Broeren and Singh (1989) indicate that 27 of these water supply systems are currently not adequate to supply water demands during a 50-year drought. Prior to 1970, the construction of a new reservoir might have been considered the principal alternative when a community's existing system was becoming inadequate. But one current trend is for these communities to develop smaller supplemental supplies for use either with the existing supply or as an emergency supply during drought conditions. The cities of Bloomington and Decatur, for example, are both evaluating the use of ground water to supplement their reservoir storage. Approximately 18 Illinois communities currently use some combination of surface water and ground water. Of these, eight actively withdraw from both surface and ground water, and ten retain their alternate supply source for emergency purposes only. Other approaches for augmenting supplies are presented by Singh and McConkey-Broeren (1990).

The western suburban fringe of the Chicago area has seen much population growth in recent decades and will likely continue growing. Between 1980 and 1990, major communities along the Fox River increased their total population from 237,000 to 297,000, a combined growth rate of more than 25 percent. High rates of population growth are expected to continue for many decades. The remaining groundwater resources in this portion of Illinois are limited, and continued increase in the use of surface water for PWS is likely.


Ground water provides approximately one-third of Illinois' population with drinking water. The sources of this water can be broken down into three major units: 1) sand and gravel, 2) shallow bedrock, and 3) deep bedrock. The principal aquifers of Illinois are shown in figure 2 of the Background chapter of this volume. The majority of the groundwater resources are centered in the northern two-thirds of Illinois. Sand- and-gravel aquifers are found along many of the major rivers and streams across the state and also within "buried bed-rock valley" systems. The buried bedrock valleys were created by the complex glacial and interglacial episodes of surface erosion in Illinois. There are also many instances of thin sand-and-gravel deposits within the unconsolidated materials above bedrock. These thin deposits are used throughout Illinois to supply small towns with their water requirements. The shallow bedrock units are more commonly used in the northern third of Illinois, whereas the deep bedrock units are most widely used in the northeastern quarter of Illinois (in and around the Chicago area). The use of these waters is highly variable throughout the state with respect to quantity and use classification. Figure 6 shows the distribution of PWS wells in Illinois.

Trends in Groundwater Use

Groundwater pumpage from facilities pumping more than 1 mgd in 1991 are detailed in figure 7. A definite decreasing pumpage trend can be noted for these facilities, primarily due to the reallocation of surface water (Lake Michigan) to the surrounding suburbs in the Chicago area. The current and past groundwater mining situation in northeastern Illinois (see the chapter on Groundwater Mining) has forced (by law) a reduction in pumpage from the deep Cambrian-Ordovician aquifer system. This pumpage had exceeded the practical sustained yield of this aquifer system (more water was being removed than was being replenished by natural processes) since the late 1950s. Within the last several years, Lake Michigan water has been piped west, replacing groundwater pumpage for many major cities. This trend is further exemplified in figure 8, which shows the pumpage of these facilities within the last 12 years for four major aquifer units: 1) sand and gravel, 2) Cambrian-Ordovician bedrock, 3) Silurian- Devonian limestone, and 4) Pennsylvanian-Mississippian bedrock. Only the Cambrian-Ordovician aquifer system shows a decline in pumpage due to the reallocation of Lake Michigan water to the Chicago region.


Water use in the state has increased a modest 27 per- cent since 1965. Most of that increase is in power generation. Water use for PWS has risen only about 7 percent during that time, less than the concurrent percentage increase in population. The number of public groundwater supply facilities within Illinois has risen significantly during that time, yet the total amount supplied by ground water remains near 25 percent.

A dependable, adequate source of water is essential to sustain the existing and potential population demands and industrial uses in Illinois. Modifications and practical management of the use of both surface and ground water have helped make this vital resource reliable in Illinois. As increases in water use are experienced at individual facilities, innovative alternative approaches to developing adequate water supplies must arise. In particular, this is likely to involve conjunctive use of surface and ground waters. Major metropolitan centers such as the Chicago area, Peoria, Decatur, and Bloomington-Normal have already developed both surface and ground water to meet their needs for development and to sustain growth. The construction of impounding reservoirs has become and will remain economically and environmentally expensive, making it a less common approach.

Proper management of water resources is also necessary to ensure a reliable, high-quality supply for the population. Water conservation practices will become increasingly important to reduce total demand and avoid exceeding available supplies. Both our groundwater resources and surface reservoir storage must be preserved to maintain reliable sources for future generations.


Broeren, S.M., and K.P. Singh. 1989. Adequacy of Illinois Surface Water Supply Systems to Meet Future Demands. Illinois State Water Survey Contract Report 477, Champaign, IL.

Gerber, W.D. 1932. The Drought of 1930 and Surface Water Supplies in Illinois. Journal of the American Water Works Association 24(6):840.

Habermeyer, G.C. 1925. Public Groundwater Sup-plies in Illinois. Illinois State Water Survey Bulletin 21 (Supplements I and II issued in 1938 and 1940), Champaign, IL.

Hanson, R. 1950. Public Groundwater Supplies in Illinois. Illinois State Water Survey Bulletin 40 (Supplements I and II issued in 1958 and 1961), Champaign, IL.

Hudson, H.E., Jr., and W.J. Roberts. 1955. The 1952- 1955 Illinois Drought with Special Reference to Impounding Reservoir Design. Illinois State Water Survey Bulletin 43, Champaign, IL.

Illinois Technical Advisory Committee on Water Resources (ITACWR). 1967. Water for Illinois: A Plan for Action. Springfield, IL.

Kirk, J.R. 1987. Water Withdrawals in Illinois, 1986. Illinois State Water Survey Circular 167, Champaign, IL.

Kirk, J.R., K.J. Hlinka, R.T. Sasman, and E.W. Sanderson. 1985. Water Withdrawals in Illinois, 1984. Illinois State Water Survey Circular 163, Champaign, IL.

Kirk, J.R., J. Jarboe, E.W. Sanderson, R.T. Sasman, and C. Lonnquist. 1982. Water Withdrawals in Illinois, 1980. Illinois State Water Survey Circular 152, Champaign, IL.

Kirk, J.R., J. Jarboe, E.W. Sanderson, R.T. Sasman, and R.A. Sinclair. 1979. Water Withdrawals in Illinois, 1978. Illinois State Water Survey Circular 140, Champaign, IL.

Kirk, J.R., E.W. Sanderson, and R.T. Sasman. 1984. Water Withdrawals in Illinois, 1982. Illinois State Water Survey Circular 161, Champaign, IL.

McConkey, S.A., A. Greene, and R. Sinclair. 1993. Geographic Information System Statewide Database for Public Surface Water Supplies in Illinois. Illinois State Water Survey report in preparation, Champaign, IL.

Singh, K.P., S.M. Broeren, R.B. King, and M.L. Pubentz. 1988. Future Water Demands of Public Water Supply Systems in Illinois. Illinois State Water Survey Con- tract Report 442, Champaign, IL.

Singh, K.P., and S.A. McConkey-Broeren. 1990. Mitigative Measures for At-Risk Public Surface Water Sup- ply Systems in Illinois. Illinois State Water Survey Contract Report 505, Champaign, IL.

Table 1. Increase in Illinois Water Use, 1965 to 1991 (mgd)

Water Use 1965 '1991

Power generation 13000 18136 Self-supplied industry 1440 614 Public water supply 1760 1886 Total 16200 20636

Table 2. Number of Public Water Supply Facilities

Surface Ground Year water Total

1925 74 398 472 1938 172 453 625 1950 111 535 646 1957 640 1960 771 1980 118 1045 1163 1985 119 1281 1400 1990 118 1285 1403

Sources: Habermeyer, 1925; Hanson, 1950; and Illinois Water Inventory Program (IWIP).

Table 3. PWS Facilities in Illinois with Surface Water as Their Primary Source

1930 1954 1970 1992

Reservoir systems 32 67 85 77

Withdrawals from streams 24 24 15 17

Direct withdrawals from border rivers 14 14 15 15

Withdrawals from Lake Michigan 10 10 14 17

Total 80 115 129 126

Note: Numbers are approximate. Sources: 1930 from Gerber, 1932; 1954 from Hudson and Roberts, 1955; 1992 from McConkey et al., 1993. 1970 estimated using data from various sources. Figure 1. Total water use for the 162 largest PWS facilities

Figure 2. Examples of increases in water use at individual facilities, 1911-1991

Figure 3. Growth in water use for four categories of surface water supply, 1961-1991

Figure 4. Location of public water supply intakes from surface water sources

Figure 5. Number of water supply reservoirs constructed in Illinois, 1900-1990

Figure 6. Location of public water supply wells in Illinois, 1900-1990

Figure 7. Total groundwater use from facilities pumping 1 mgd or more in 1991

Figure 8. Total groundwater use from major aquifer units by facilities pumping 1 mgd or more in 1991

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