But most commonly, we obtain ground water from wells. Most ground water is constantly moving, but it normally moves very slowly as it winds its way through tiny pathways around grains of sediment or through small openings in rock. In certain restricted areas, such as portions of southeastern Minnesota, carbonate rock formations have developed cave-like openings that allow ground water to move much faster like an underground river. Ground water can move fairly rapidly through coarser, uncemented sediments composed of gravel and sand. The ability to transmit ground water is reduced where the sediments are made up of finer materials, such as silt and clay.
Caves allow water to move quickly.
However, in practice, the process of drilling the boring and properly installing the well can be a very complicated task. First, an aquifer must be located. When a water-supply well is desired, the drillers are usually looking for a subsurface zone that is highly permeable and has good quality water. However, specially-designed wells called monitoring wells may be installed in a variety of subsurface zones soley to measure water levels or to test for contamination. In either case, the well must have openings set at just the right depth to only let ground water from the desired subsurface zone into the well.