Groundwater

Groundwater is the <a href="/facts/Water/0lkXnJPK">water</a> present beneath <a href="/facts/Earth/HLLmDfj0">Earth</a>'s surface in rock and <a href="/facts/Pore_space_in_soil/aLuyMtU6">soil pore spaces</a> and in the <a href="/facts/Fracture/nxDNAj0d">fractures</a> of <a href="/facts/Stratum/w5D4VAwa">rock formations</a>. About 30 percent of all readily available <a href="/facts/Fresh_water/xMP2TxwI">fresh water</a> in the world is groundwater. A unit of rock or an unconsolidated deposit is called an <a href="/facts/Aquifer/UwG6ksdG">aquifer</a> when it can yield a usable quantity of water. The depth at which <a href="/facts/Soil/5Ddpr3QM">soil</a> pore spaces or <a href="/facts/Fracture/nxDNAj0d">fractures</a> and voids in rock become completely saturated with water is called the <a href="/facts/Water_table/2j0VD0lF">water table</a>. Groundwater is <a href="/facts/Groundwater_recharge/el8C40xD">recharged</a> from the surface; it may discharge from the surface naturally at <a href="/facts/Spring_(hydrosphere)/blPBY4VG">springs</a> and <a href="/facts/Seep_(hydrology)/ym78k7Jn">seeps</a>, and can form <a href="/facts/Oasis/BT9IVsR7">oases</a> or <a href="/facts/Wetland/9abbP7CR">wetlands</a>. Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction <a href="/facts/Water_well/aPFvzk3V">wells</a>. The study of the distribution and movement of groundwater is <a href="/facts/Hydrogeology/4HEanFa0">hydrogeology</a>, also called groundwater <a href="/facts/Hydrology/Xh727cnE">hydrology</a>.
Typically, groundwater is thought of as water flowing through shallow aquifers, but, in the technical sense, it can also contain <a href="/facts/Soil_moisture/N9Yo068u">soil moisture</a>, <a href="/facts/Permafrost/SkFC7LMT">permafrost</a> (frozen soil), immobile water in very low permeability <a href="/facts/Bedrock/mn9WCgtX">bedrock</a>, and deep <a href="/facts/Geothermal_activity/8lUW53Yv">geothermal</a> or <a href="/facts/Petroleum_geology/jMPyPVmN">oil formation</a> water. Groundwater is hypothesized to provide <a href="/facts/Lubrication/6tHKQVqy">lubrication</a> that can possibly influence the movement of <a href="/facts/Fault_(geology)/0Fw2ladx">faults</a>. It is likely that much of <a href="/facts/Earth/HLLmDfj0">Earth</a>'s subsurface contains some water, which may be mixed with other fluids in some instances. 
Groundwater is often cheaper, more convenient and less vulnerable to <a href="/facts/Water_pollution/SCUhUYqB">pollution</a> than <a href="/facts/Surface_water/KQCY5RcY">surface water</a>. Therefore, it is commonly used for public <a href="/facts/Drinking_water/FmSJcKGG">drinking water</a> supplies. For example, groundwater provides the largest source of usable water storage in the <a href="/facts/United_States/P0sCdLe5">United States</a>, 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 <a href="/facts/Great_Lakes/Fd7pDkPX">Great Lakes</a>. Many municipal water supplies are derived solely from groundwater. Over 2 billion people rely on it as their primary water source worldwide.
Human use of groundwater causes environmental problems. For example, <a href="/facts/Groundwater_pollution/9tcqXv2B">polluted groundwater</a> is less visible and 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 <a href="/facts/Industrial_chemical/3M6gfHer">industrial</a> and <a href="/facts/Household_chemicals/E9NyWQy0">household chemicals</a> and garbage <a href="/facts/Sanitary_landfill/7K4efGgz">landfills</a>, excessive <a href="/facts/Fertilizer/ysh3r6NJ">fertilizers</a> and pesticides used in agriculture, industrial waste lagoons, tailings and process <a href="/facts/Wastewater/g6Bn8xvT">wastewater</a> from mines, industrial <a href="/facts/Fracking/cCTzfwkg">fracking</a>, oil field brine pits, leaking underground oil storage tanks and pipelines, <a href="/facts/Sewage_sludge/qztXxBSD">sewage sludge</a> and <a href="/facts/Septic_tank/hHgN3sM3">septic systems</a>. Additionally, groundwater is susceptible to <a href="/facts/Saltwater_intrusion/kTNApmu0">saltwater intrusion</a> in coastal areas and can cause <a href="/facts/Land_subsidence/EIwtz9w9">land subsidence</a> when extracted unsustainably, leading to <a href="/facts/Sinking_cities/0jUozCB9">sinking cities</a> (like <a href="/facts/Bangkok/WRxftcFz">Bangkok</a>) and loss in elevation (such as the <a href="/facts/Central_Valley_land_subsidence/eupxkVpj">multiple meters lost in the Central Valley of California</a>). These issues are made more complicated by <a href="/facts/Sea_level_rise/Pb5MGJxb">sea level rise</a> and other <a href="/facts/Effects_of_climate_change/M5EvHf14">effects of climate change</a>, particularly <a href="/facts/Effects_of_climate_change_on_the_water_cycle/0USCzHgt">those on the water cycle</a>. Earth's <a href="/facts/Axial_tilt/kt7KwL3v">axial tilt</a> has shifted 31 inches because of human groundwater pumping.

Groundwater open-in-new

Groundwater