Aquifer-performance tests and aquifer studies indicate that the limestone beneath the city of Adel and probably most of Cook County contains potable water to a depth of only about 400 to 500 feet and that "deep" wells that tap these limestones obtain most of their water from a few thin, highly permeable zones rather than from the entire thickness of the rocks. Below about 500 feet the water is mineralized and not potable without treatment. The yield of "shallow wells" is variable and the water generally is corrosive and at places contains appreciable dissolved iron.
The volume of ground water flowing through the Suwannee and Marianna Limestones in Cook County and available for development to properly spaced wells and well fields is estimated to be about 18,000,000 gallons per day. That in the Tampa Foundation is estimated to be about 1,500,000 gallons per day.
Water levels near the center of the Adel well field have declined 38 feet since 1890 and presently are declining at a rate of 1.6 feet per year.