Population growth in Walworth County, Wisconsin, requires an increasing amount of ground water. Good quality water is available from the sand-and gravel, Niagara, Galena-Platteville, and sandstone aquifers in the county. As much as 15 gallons per minute (0.95 liters per second) can be obtained from individual wells almost everywhere in the county. Well yields of 1,000 gallons per minute (63 liters per second) are available from glacial drift where it contains sufficient thickness of saturated sand and gravel. The sand-and-gravel aquifer is an important source of municipal water. Estimated well yields from most of the Niagara aquifer, a Silurian age dolomite as thick as 125 feet (38.1 meters), exceed 100 gallons per minute (6.3 liters per second). The Niagara aquifer occurs in the eastern third of the county. The Galena-Platteville aquifer, chiefly dolomite, is present in the western half of the county where it is as thick as 325 feet (99.1 meters). Estimated yields from this aquifer exceed 500 gallons per minute (32 liters per second). The sandstone aquifer underlies the entire county and ranges from less than 800 feet (240 meters) thick in the northwest corner to more than 2,200 feet (670 meters) in the east. This aquifer is capable of yielding 1,000 gallons per minute (63 liters per second) to individual wells and is a principal source of municipal water.