Claim: 1.7% of water can be found in underground.

Groundwater -LRB- or ground water -RRB- is the water present beneath Earth 's surface in soil pore spaces and in the fractures of rock formations . A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water . The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table . Groundwater is recharged from , and eventually flows to , the surface naturally ; natural discharge often occurs at springs and seeps , and can form oases or wetlands . Groundwater is also often withdrawn for agricultural , municipal , and industrial use by constructing and operating extraction wells . The study of the distribution and movement of groundwater is hydrogeology , also called groundwater hydrology .   Typically , groundwater is thought of as water flowing through shallow aquifers , but , in the technical sense , it can also contain soil moisture , permafrost -LRB- frozen soil -RRB- , immobile water in very low permeability bedrock , and deep geothermal or oil formation water . Groundwater is hypothesized to provide lubrication that can possibly influence the movement of faults . It is likely that much of Earth 's subsurface contains some water , which may be mixed with other fluids in some instances . Groundwater may not be confined only to Earth . The formation of some of the landforms observed on Mars may have been influenced by groundwater . There is also evidence that liquid water may also exist in the subsurface of Jupiter 's moon Europa .   Groundwater is often cheaper , more convenient and less vulnerable to pollution than surface water . Therefore , it is commonly used for public water supplies . For example , groundwater provides the largest source of usable water storage in the United States , and California annually withdraws the largest amount of groundwater of all the states . Underground reservoirs contain far more water than the capacity of all surface reservoirs and lakes in the US , including the Great Lakes . Many municipal water supplies are derived solely from groundwater .   Polluted groundwater is less visible , but more difficult to clean up , than pollution in rivers and lakes . Groundwater pollution most often results from improper disposal of wastes on land . Major sources include industrial and household chemicals and garbage landfills , excessive fertilizers and pesticides used in agriculture , industrial waste lagoons , tailings and process wastewater from mines , industrial fracking , oil field brine pits , leaking underground oil storage tanks and pipelines , sewage sludge and septic systems .