Rochester’s earliest residents used surface water taken from the rivers to meet their personal and industrial needs. Today, Rochester’s water supply is extracted from bedrock aquifers - large rock formations that hold water in small fractures within the rock layers or in the pore spaces between the particles that form the rock. Fractured limestone and porous sandstone are the aquifer forming rocks in the Rochester area. To be a dependable source of water, aquifers must be both porous, (meaning there are spaces for the water to be in) and permeable, (the water can move easily through the rock). Most of Rochester’s water comes from the Jordan Aquifer which is composed of sandstone. Rochester sometimes also uses other aquifers such as the St Peter, Prairie du Chien limestone, the Ironton-Galesville sandstone, and the Mt. Simon sandstone.
Water from the underground aquifers is drawn to the surface by 33 wells located throughout the city. In 2012, the average amount of water pumped by the City of Rochester was 13,183,000 gallons each day. The total amount of water pumped during 2012 was 4,825,000,000 gallons. This total was about 6 percent less than the record of 5,110,000,000 gallons set in 2007 for yearly volume pumped.
Even though the quality of the water supply is good today, the local geology presents risks for contamination. Where the underlying soils and bedrock are both permeable, the wells are vulnerable to pollution. The thicker and the less permeable the soil layer, the more the filtering capacity, reducing the risk for groundwater pollution. Thus, our actions on the land can have a direct impact on the quality of our groundwater supply.