Water distributed by municipal systems has been the largest off-stream use of water in southeastern Minnesota for the past 100 years. Water pumped by these systems in 1980 totaled 102.3 billion gallons, with 60.1 billion gallons supplied by ground water. Ground water supplies 294 of the 309 municipal systems in the area.

The development of ground-water supplies for municipal use in southeastern Minnesota began around the 1880's as an alternative to supplies from lakes and rivers. After about 4,500 Minnesotans died from typhoid from 1891 to 1900, deep wells became widely used in order to avoid contaminated surface water.

An inventory of 1,244 wells drilled for municipal systems from 1880 to 1980 has been completed. Of the five bedrock aquifers in the study area, the Prairie du Chien-Jordan is the most extensively used for water supply; 537 municipal wells tap it. About half of these wells were drilled in the Twin Cities Metropolitan Area since 1945 to accommodate suburban growth. The undifferentiated drift aquifer ranks second in use with 294 municipal wells tapping it. Most of these wells are completed in aquifers buried in thick drift deposits in the western part of the study area.

Aquifer preference was analyzed to determine whether municipal wells were completed in the shallowest bedrock aquifer present in an area, in a deeper bedrock aquifer, or in a drift aquifer above the bedrock. Until 1950, there was a strong preference to complete municipal wells in the Upper Carbonate aquifer. Because of poor water quality in parts of the aquifer, most municipal wells drilled in the area since 1950 are cased through the Upper Carbonate and completed in deeper aquifers. The St. Peter aquifer is little used for municipal wells because wells completed in it often pump sand. About 96 percent of the municipal wells drilled in the St. Peter aquifer subcrop area since 1950 were cased through the St. Peter and completed in deeper aquifers. About 64 percent of the municipal wells drilled in the Mount Simon-Hinckley aquifer subcrop area are completed in drift aquifers. The Prairie du Chien-Jordan and Ironton-Galesville aquifers are preferred for municipal wells in their respective areas of occurrence.

Water appropriation in Minnesota is regulated through a permit system based on five water-use priorities. Domestic water supply, excluding industrial and commercial uses of a municipal water supply, is the highest priority (Minnesota Statutes, Chapter 105.41). Under the regulations, uses of a lower priority are not permitted to adversely affect uses of a higher priority. Identification of the aquifer(s) used for municipal supplies is also necessary to safeguard these supplies from adverse effects of competing water users and contamination, and to evaluate the consequences of each.