ILLINOIS WATER SUPPLY
In Illinois there are about 332 municipal water works systems. About 79 per cent, of the cities and villages of 1,000 or more are provided with public water supplies. Not including Chicago, the aggregate population of these towns having water works is slightly over 1,630,000. The majority of these supplies are derived from wells, but over 40 per cent, of this population is supplied with surface water. Chicago, which pumps its supply from Lake Michigan, is left out of consideration in compiling the accompanying data for the reason that its great size would tend toward distortion of general averages and conclusions relative to the numerous small supplies. The character of the supply chosen by a town in Illinois depends largely upon the section of the state the town happens to occupy. In a general way, a good supply can most economically be obtained from wells, but in some regions ground water is to be had only in very limited quantities or is found to be of inferior quality from a mineral standpoint. Along the shores of Lake Michigan, comparatively good well water is to be had in deep drillings, but in only one instance, namely, Lake Bluff, has a town such a source of supply in preference to the lake. In the northern quarter of the state good supplies are to be had from the St. Peter’s and Potsdam sandstone. The former ranges in depth from about 600 to 1,500 feet, while the latter is usually at a depth of 300 to 500 feet below the St. Peter’s. In the central part of the state, wells drilled to these strata usually yield very highly mineralized water, frequently charged with hydrogen sulphide. Central Illinois, however, is favored with having a heavy deposit of drift which yields an abundant supply of water in most localities. But these deposits of water-bearing gravel arc also limited in extent. In a general way to the south of a line running east and west through Champaign, water is seldom obtainable in large quantities from either deep rock or drift wells and such ground water as is found is usually very hard. Exceptions to this rule exist near the southern extremity of the state, exemplified by Anna and Mounds, where excellent supplies are obtained from deep drillings in limestone. But it is frequently the case that there is practically no choice but to adopt a surface supply in southern Illinois. All Illinois ground waters are comparatively hard, seldom having less than 300 parts per million of dissolved solids. For small communities this water, when obtainable, is, however, often preferable to a surface supply. There is no surface water in the state, except Lake Michigan at a distance of five miles or over from shore, that is satisfactory for domestic uses at all times without purification. All surface supplies are subject to more or less pollution and there are hardly any that are not excessively turbid at times. From investigations made, it has been found that out of about 332 cities and villages having public water supplies. 41.5 per cent, of their population is supplied with water of surface origin. About 73.4 per cent, of the population using surface water is supplied with water treated in some manner for the purpose of clarifying or sterilizing the supply. The effectiveness of these treatment processes, of course, varies widely. In a large number of towns using surface water, the principal value of the supply is considered to lie in its use for fire protection. Most of the older towns of the state at some distance from Chicago began with a general use of private wells and they have been slow to give them up following the installation of municipal supplies. The unpurified supplies of southern. Illinois seems to he very little used for drinking purposes, and only to a limited extent for other domestic uses, which is not surprising, considering their frequently high turbidity. The smaller communities on the North. Shore taking their supplies from Lake Michigan use the water very extensively, notwithstanding its unsatisfactory quality. This is probably due to the fact that these populations are made up of people who have always lived in cities and demand such conveniences as public water supplies and indoor plumbing.
• Reprinted from Illinois State Water Survey Bulletin.