Well Water
Private Well Water Guide
Over 43 million Americans rely on private wells. Unlike public water systems, private wells are not federally regulated — testing, treatment, and maintenance are entirely the homeowner's responsibility.
Private wells have no mandatory testing requirements. The EPA recommends annual testing at minimum.
Why This Matters
Public water systems serving 25 or more people are regulated under the Safe Drinking Water Act and must test water regularly, report results to the public, and fix violations. Private wells serving fewer than 25 people have none of these requirements. Contamination that would trigger a public health notice for a utility can go undetected in a private well for years.
How to Approach Well Water Testing
Test annually at minimum
Coliform bacteria and nitrates should be tested every year regardless of state. Most certified labs offer a basic well panel for $75–$200.
Know your local risks
Your state geology, nearby agriculture, and industrial history determine which additional tests matter. Select your state below for a specific risk profile.
Use a certified lab
Standard home test kits are unreliable for health-based contaminants. Use a state-certified or NELAP-accredited laboratory for results you can act on.
Retest after any change
Heavy rain events, nearby construction, flooding, changes in taste/odor/color, or new neighbors with septic systems are all triggers for retesting.
What to Test For — Common Well Water Contaminants
The right tests depend on your location, nearby land use, and well age. These are the most commonly detected or risk-relevant contaminants across U.S. private wells.
Coliform Bacteria
Universal risk — always test annually
Nitrates
Agricultural areas especially — infant risk
Arsenic
Southwest, West — naturally occurring
Lead
Old well casings, pre-1986 household plumbing
PFAS
Near military bases, airports, industrial sites
Radon
Granite geology, Northeast, Southeast
Hardness
Equipment and plumbing — not a health hazard
Iron & Manganese
Taste, staining — aesthetic concern
State-Specific Well Water Guides
Contaminant risks, testing requirements, and lab referral programs vary by state. Select your state for location-specific guidance.
California Well Water Guide
Approximately 10% of Californians — over 4 million people — rely on private wells for drinking water. California's diverse geology creates region-specific contamination risks: naturally occurring arsenic and uranium in the Central Valley and foothills, nitrate contamination from intensive agriculture, PFAS near military installations, and hexavalent chromium (chromium-6) in several inland regions. The State Water Resources Control Board oversees small water systems, but private domestic wells are the responsibility of the homeowner.
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Texas Well Water Guide
Texas has approximately 1.5 million private water wells, with rural and suburban residents across the Hill Country, West Texas, and the Panhandle commonly relying on groundwater. The state's primary well water concerns include naturally occurring arsenic (particularly in West Texas and the Hill Country), high nitrates from agricultural and septic sources, radium and uranium in granite-dominated regions, and bacterial contamination in shallow alluvial wells. The Texas Commission on Environmental Quality (TCEQ) oversees public water systems; private wells are the landowner's responsibility.
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Florida Well Water Guide
Florida has over 1 million private wells, with use concentrated in rural areas of North and Central Florida. Florida's unique geology — primarily porous karst limestone (the Floridan Aquifer System) — creates both the state's water abundance and its contamination vulnerabilities. Key concerns include naturally occurring radium, uranium, and radon from phosphate-rich limestone, nitrate and bacterial contamination from septic systems and agricultural runoff, and legacy contamination from the phosphate mining industry in the central state.
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Arizona Well Water Guide
Arizona's private well users — primarily in rural areas outside the Phoenix and Tucson metro served areas — face some of the most challenging well water conditions in the nation. The state's arid geology concentrates naturally occurring contaminants including arsenic, uranium, fluoride, and chromium-6 in groundwater. Aquifer overdraft is also a serious concern, with many rural Arizona wells experiencing declining water levels. The Arizona Department of Environmental Quality (ADEQ) regulates public water systems; private domestic wells (fewer than 5 service connections) are minimally regulated.
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Ohio Well Water Guide
Ohio has over 800,000 private wells serving approximately 2 million residents, concentrated in rural areas outside municipal water service areas. Ohio's glacial geology, agricultural intensity, and legacy industrial history create a complex contamination landscape. Primary concerns include nitrate from agriculture and septic systems, bacteria from karst geology in northwest Ohio and the limestone belt, lead from older well pump and pressure tank components, and PFAS from industrial sources concentrated in the northeastern and central portions of the state.
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Alabama Well Water Guide
About 36% of Alabama residents — over 1.7 million people — rely on private wells, one of the highest rates in the Southeast. Alabama's karst limestone geology in the northern part of the state makes groundwater highly vulnerable to contamination from surface sources, as water moves quickly through sinkholes and underground channels with minimal natural filtration. Primary concerns include bacterial contamination, nitrates from agriculture and failing septic systems, iron and manganese staining, and localized PFAS plumes near industrial and military sites.
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Oregon Well Water Guide
Approximately 27% of Oregon residents — about 1.1 million people — rely on private wells. Oregon's well water risks vary dramatically by region: western Oregon's high rainfall creates bacterial and nitrate risks from agricultural runoff, while eastern Oregon's basalt geology contributes naturally occurring arsenic and uranium. The Willamette Valley — Oregon's most populated agricultural region — has documented nitrate contamination in shallow wells. PFAS plumes have been identified near several military and industrial sites. The Oregon Health Authority oversees well construction but not ongoing private well testing.
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Pennsylvania Well Water Guide
Approximately 26% of Pennsylvania residents — about 3.3 million people — rely on private wells, making Pennsylvania one of the largest private well populations on the East Coast. Pennsylvania's geology creates diverse contamination risks: naturally occurring radon and radium in granite areas, arsenic in the southeast and northwest, iron and manganese statewide, and significant PFAS contamination near military installations and industrial sites. The Marcellus Shale natural gas drilling boom has also raised methane migration and spill contamination concerns for rural wells. Pennsylvania does not require private well testing, leaving the burden on individual homeowners.
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Washington Well Water Guide
Approximately 20% of Washington residents — about 1.5 million people — rely on private wells or small water systems. Well water risks divide sharply between western and eastern Washington: western Washington's high rainfall creates bacterial and turbidity risks in shallow wells, while eastern Washington's agricultural areas (Columbia Basin, Yakima Valley) have documented nitrate contamination, and the basalt geology contributes naturally occurring arsenic and fluoride. PFAS contamination has been documented near Joint Base Lewis-McChord and Fairchild AFB. Washington State has one of the more active private well programs in the country.
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Nevada Well Water Guide
Approximately 10% of Nevada residents rely on private wells, concentrated in rural counties across the Great Basin. Nevada's arid geology creates a distinct contamination profile: naturally occurring arsenic is widespread across the Basin and Range geology, fluoride is elevated in some volcanic aquifers, and uranium has been documented in portions of the Colorado River watershed. The absence of regular recharge in Nevada's desert aquifers means some contamination from mining operations and legacy industrial sites persists for decades. The Nevada Division of Environmental Protection oversees well construction standards, but private well owners are responsible for water quality monitoring.
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Kansas Well Water Guide
Approximately 28% of Kansas residents — nearly 800,000 people — rely on private wells. Kansas sits atop the High Plains (Ogallala) Aquifer — one of the world's largest — but intensive agriculture has significantly degraded water quality in shallow layers. Nitrate contamination is the dominant concern, with some of the highest agricultural nitrate concentrations in the U.S. documented in central and western Kansas. Atrazine (a widely used herbicide) contamination in shallow wells is also a significant issue. Naturally occurring arsenic is present in some aquifer layers. The Kansas Department of Health and Environment (KDHE) provides well construction oversight but not ongoing monitoring requirements.
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Kentucky Well Water Guide
Approximately 30% of Kentucky residents — about 1.3 million people — rely on private wells. Kentucky's geology creates one of the most complex well water situations in the nation: widespread karst limestone in the central and western parts of the state makes groundwater extremely vulnerable to rapid surface contamination, while eastern Kentucky's coal country adds legacy mining contamination including acid mine drainage, selenium, and iron. The Bluegrass region has naturally occurring elevated radon. Agricultural nitrate contamination is documented in multiple counties. The Kentucky Division of Water oversees well construction but does not mandate private well testing.
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New Mexico Well Water Guide
Approximately 15% of New Mexico residents — about 300,000 people — rely on private wells and small systems. New Mexico's arid geology creates a distinct contamination profile dominated by naturally occurring contaminants: arsenic is widespread in volcanic and basin geology across the state, uranium is naturally elevated in sandstone aquifers in the Grants Mineral Belt and eastern New Mexico, and fluoride exceeds recommended levels in some southwestern aquifers. The state also has significant legacy uranium mining contamination on the Navajo Nation and in the Grants Belt, affecting both private wells and small community systems. The New Mexico Environment Department (NMED) oversees well construction but private domestic wells are exempt from ongoing regulatory monitoring.
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Maine Well Water Guide
Nearly half of Maine residents — over 650,000 people — rely on private wells drilled into or dug from Maine's ancient granite and metamorphic bedrock. Maine has some of the highest naturally occurring arsenic concentrations in New England, with approximately 10% of tested private wells exceeding the EPA limit of 10 ppb. Radon dissolved in water (distinct from airborne radon) is also prevalent statewide. The Maine Center for Disease Control & Prevention (MECDC) recommends all new and existing wells be tested comprehensively, and retested after any flood or nearby construction.
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New Hampshire Well Water Guide
New Hampshire has the highest proportion of residents relying on private wells of any New England state — approximately 55%, or over 700,000 people. The state's granite bedrock is a source of naturally occurring arsenic (approximately 10–15% of wells exceed 10 ppb), radon, and uranium. New Hampshire is also home to one of the most extensively studied PFAS contamination sites in the U.S.: Pease International Tradeport in Portsmouth, a former U.S. Air Force base where PFAS from AFFF firefighting foam contaminated the municipal supply and nearby private wells. NH DES provides one of the more proactive state private well programs in the region.
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Vermont Well Water Guide
Approximately half of Vermont residents rely on private wells for drinking water. Vermont's geology — Green Mountain metamorphic and granitic rock in the east, limestone and dolomite in the Champlain Valley — creates distinct contamination patterns by region. Arsenic is documented in wells across both the crystalline bedrock and the carbonate Champlain Valley geology. Vermont is also home to a significant documented PFAS contamination site in Bennington, where manufacturing by Saint-Gobain Performance Plastics contaminated private wells and the municipal supply with PFOA. Vermont has its own PFAS MCL of 20 ppt (sum of six compounds), stricter than the federal standard.
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Massachusetts Well Water Guide
Approximately 18% of Massachusetts residents — around 1.2 million people — rely on private wells. Massachusetts' crystalline granite bedrock generates naturally occurring arsenic and radon, while the Cape Cod region faces nitrate contamination from high-density septic systems and a legacy of PFAS from Joint Base Cape Cod (formerly Otis Air National Guard Base). Massachusetts has among the strictest PFAS standards in the nation (20 ppt sum of six compounds) and was among the first states to document widespread PFAS in drinking water. The MA DEP certifies labs for private well testing and offers guidance through its Private Well Owner Resources program.
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Connecticut Well Water Guide
Approximately 22% of Connecticut residents rely on private wells, with the highest concentrations in eastern and northwestern Connecticut. Connecticut's granite and metamorphic bedrock releases naturally occurring arsenic, radon, and uranium — with radon-in-water levels among the highest in the nation for affected wells. Industrial legacy contamination is significant: Connecticut's Naugatuck River Valley and other industrial corridors have well-documented VOC plumes from former metal manufacturing and plating operations. Connecticut DPH certifies labs and provides well testing guidance through the Private Well Testing Act, which requires testing at point of sale.
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Rhode Island Well Water Guide
Rhode Island is the most densely populated state with a significant private well population — approximately 12% of residents, or about 125,000 people, rely on private wells. Most private well users are in Kent, Washington, and Providence counties. Rhode Island's geology includes granite bedrock in the northern third of the state and glacial outwash deposits across much of the state. Arsenic from granite is a documented concern, as is PFAS from Quonset State Airport and former naval activities at Naval Air Station Quonset Point. The RI DEM certifies labs and provides guidance under the Private Well Regulation Act.
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New York Well Water Guide
About 2.6 million New Yorkers rely on private wells, concentrated in rural upstate counties, Long Island, and suburban areas outside NYC's water distribution network. New York's geology creates localized contamination risks: naturally occurring arsenic and uranium in the Adirondacks and Hudson Valley, PFAS from industrial sites and military bases, trichloroethylene (TCE) and other solvents from manufacturing, and saltwater intrusion on Long Island. The NYS Department of Health provides voluntary guidance but does not mandate testing for private wells.
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New Jersey Well Water Guide
Approximately 1.7 million New Jerseyans — about 20% of the population — rely on private wells, primarily in rural and suburban areas of Burlington, Morris, Monmouth, Ocean, and Sussex counties. New Jersey's industrial legacy and dense development make it one of the more contamination-prone states for private wells. PFAS, TCE, arsenic in northern bedrock, radon, and nitrates from dense septic development are the primary concerns. NJDEP administers the Private Well Testing Act, which requires testing at point of sale.
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Delaware Well Water Guide
About 24% of Delawareans rely on private wells, primarily in Sussex County's rural and coastal communities and parts of Kent County. Delaware's shallow coastal plain aquifers are highly vulnerable to agricultural contamination: nitrates from poultry farming and crop production are the state's most pervasive groundwater concern. PFAS from Dover Air Force Base and industrial sites, iron and manganese from coastal plain sediments, and saltwater intrusion in coastal areas are additional risks. DNREC provides well permitting and limited oversight.
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Maryland Well Water Guide
About 25% of Marylanders — approximately 1.5 million people — rely on private wells, primarily in the rural Eastern Shore, Western Maryland, and suburban fringes of the Washington DC and Baltimore metro areas. Maryland's diverse geology creates distinct regional risks: arsenic and radon in the crystalline rock of Frederick and Carroll counties, nitrates and agricultural contaminants on the Eastern Shore, PFAS from military installations, and iron/manganese throughout the coastal plain. Maryland's Environmental Regulations require certain well construction standards but do not mandate ongoing testing.
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Virginia Well Water Guide
Approximately 2.3 million Virginians rely on private wells — about 28% of the state's population. Virginia's geography creates highly variable groundwater quality: crystalline rock in the Blue Ridge and Piedmont contains natural arsenic and uranium; the Coastal Plain's shallow aquifers are vulnerable to agricultural and septic contamination; and numerous military installations contribute PFAS contamination. VDH regulates well construction but does not mandate ongoing water quality testing for existing private wells.
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West Virginia Well Water Guide
West Virginia has one of the highest rates of private well reliance in the eastern US — approximately 38% of residents use private wells, with usage concentrated in the rural Appalachian counties that make up most of the state. Coal mining and natural gas extraction create unique contamination risks: acid mine drainage, heavy metals from coal seams, and methane from oil and gas operations can affect groundwater quality. Naturally occurring iron, manganese, and sulfates from geological sources are also pervasive. WVDHHR regulates well construction but testing is voluntary for existing wells.
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North Carolina Well Water Guide
About 2.5 million North Carolinians — 35% of the state — rely on private wells. North Carolina faces a significant PFAS challenge: the state is home to some of the most contaminated PFAS groundwater sites in the nation, particularly from Chemours' Fayetteville Works facility (GenX contamination) and military installations across the state. Additionally, naturally occurring arsenic and uranium in the Piedmont and Mountain crystalline rocks, agricultural nitrates in the Coastal Plain, and radium in the eastern coastal plain aquifers create multi-faceted risks. NCDHHS and NCDEQ provide oversight but do not mandate private well testing.
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South Carolina Well Water Guide
About 30% of South Carolinians rely on private wells, primarily in rural Lowcountry, Pee Dee, and Upstate communities. South Carolina's coastal plain aquifers naturally contain elevated iron, manganese, and radium. Agricultural contamination from poultry and swine operations in the Pee Dee region contributes significant nitrate loading. PFAS from military installations, including Shaw AFB and Marine Corps Air Station Beaufort, affect areas of Sumter and Beaufort counties. SCDHEC provides well construction standards and voluntary testing guidance.
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Georgia Well Water Guide
About 2.8 million Georgians — 28% of the population — rely on private wells, with the highest rates in rural north Georgia mountains, the agricultural southeast, and suburban fringe communities. North Georgia's crystalline metamorphic and igneous rocks contain naturally elevated arsenic. The Dougherty Plain's karst limestone aquifer in southwest Georgia is highly vulnerable to agricultural and bacterial contamination. Coastal plain aquifers in south Georgia have naturally elevated iron, manganese, and occasionally radium. EPD regulates well construction but does not require periodic testing.
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Tennessee Well Water Guide
About 22% of Tennesseans rely on private wells, primarily in rural east Tennessee mountain communities, middle Tennessee agricultural areas, and underserved rural west Tennessee communities. Tennessee's karst limestone geology — particularly the Central Basin's Nashville Dome — creates a highly permeable aquifer system vulnerable to surface contamination. East Tennessee's crystalline Appalachian geology produces natural arsenic risks. Agricultural contamination from livestock operations is the most pervasive statewide threat. TDEC regulates well construction but does not mandate ongoing testing.
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Mississippi Well Water Guide
Approximately 30% of Mississippians rely on private wells, concentrated in rural agricultural areas across the Delta, Piney Woods, and Hills regions. Mississippi's shallow coastal plain aquifers are among the most vulnerable in the Southeast: the Mississippi Alluvial Aquifer (Delta) is heavily affected by agricultural contamination, while the Sand/Gravel aquifer system shows naturally elevated arsenic in parts of south Mississippi. MDEP regulates well construction; testing is voluntary for private well owners but strongly recommended given the agricultural contamination prevalence.
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Arkansas Well Water Guide
About 32% of Arkansans rely on private wells, with the highest rates in the rural Ozarks, Ouachita Mountains, and agricultural Delta region. Arkansas faces diverse groundwater contamination challenges: Ozarks karst aquifers are highly vulnerable to surface contamination, Delta alluvial aquifers show agricultural contamination patterns similar to the Mississippi Delta, and naturally elevated arsenic and manganese are found throughout the Mississippi Alluvial Plain. ADEQ regulates well construction but does not mandate periodic testing for existing private wells.
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Louisiana Well Water Guide
About 18% of Louisianans rely on private wells, primarily in rural north Louisiana, the Florida Parishes (east of the Mississippi River), and some coastal communities. Louisiana's geology presents a complex groundwater picture: the Chicot aquifer system in southwest Louisiana has naturally elevated arsenic; the Carrizo-Wilcox aquifer in north Louisiana provides good quality water with occasional iron and manganese; and coastal plain aquifers face saltwater intrusion risk in the south. The state's industrial corridor (Cancer Alley) along the Mississippi River creates significant PFAS and industrial chemical concerns for some well users. LDHH provides well construction oversight.
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Illinois Well Water Guide
About 20% of Illinoisans rely on private wells, concentrated in rural agricultural counties downstate and suburban fringe communities outside Chicago's water service area. Illinois's groundwater reflects its heavy agricultural use: nitrate contamination from corn and soybean production is the most pervasive statewide concern. Naturally occurring radium in some deep sandstone aquifers, arsenic from glacial deposits in specific areas, and PFAS from industrial and military sites are additional concerns. IDPH regulates well construction; the Private Sewage Disposal Code governs septic proximity.
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Indiana Well Water Guide
About 30% of Hoosiers — approximately 2 million people — rely on private wells, with the highest rates in rural agricultural counties, the southern Indiana hill country, and exurban communities. Indiana's primary groundwater concerns mirror its land use: nitrate contamination from intensive corn and soybean farming, bacterial contamination from livestock operations and failing septic systems, and naturally elevated arsenic in specific glacial deposits. PFAS from military facilities and IDEM-regulated industrial sites are additional concerns. IDEM and the State Department of Health jointly oversee well standards.
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Iowa Well Water Guide
About 35% of Iowans rely on private wells — roughly one million people — with the highest rates in rural agricultural counties that cover most of the state. Iowa faces one of the nation's most severe agricultural groundwater contamination challenges: nitrate concentrations in Iowa's shallow aquifers are among the highest in the country due to the state's intensive corn production and heavy nitrogen fertilizer use. Bacterial contamination from livestock and manure application, and naturally elevated uranium and radium in some Cambrian-Ordovician aquifer areas, are additional concerns. IDNR regulates well construction and the state has an active private well program.
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Michigan Well Water Guide
Michigan has one of the highest rates of private well use in the Great Lakes region — about 42% of residents, or roughly 4 million people, rely on private wells. Michigan's diverse geology creates varied contamination risks: arsenic in specific glacial outwash deposits (particularly in the Kent County and nearby areas), PFAS contamination from numerous industrial and military sites (including the Plainfield Township PFAS crisis and Wurtsmith AFB), naturally elevated radon in some areas, and agricultural nitrate and bacterial contamination in rural counties. The Michigan PFAS Action Response Team (MPART) has been nationally recognized for its aggressive monitoring program. EGLE regulates well construction under Part 127 of the Michigan Public Health Code.
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Minnesota Well Water Guide
About 35% of Minnesotans — approximately 1.9 million people — rely on private wells. Minnesota has one of the most robust state private well programs in the nation, including a well disclosure requirement at real estate transfer and an extensive Drinking Water Protection Program. Primary groundwater concerns include nitrate contamination from corn and livestock agriculture in southern Minnesota, arsenic from iron-rich glacial sediments in specific regions, coliform bacteria, and PFAS from 3M's Twin Cities manufacturing operations — which contaminated eastern Metro wells and led to one of the largest PFAS settlements in U.S. history.
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Wisconsin Well Water Guide
About 38% of Wisconsinites — approximately 2.2 million people — rely on private wells. Wisconsin's private well contamination landscape is shaped by its heavy dairy farming: nitrate contamination from manure and fertilizer application is pervasive, and bacterial contamination from livestock operations affects many shallow wells. Naturally occurring arsenic in specific glacial outwash deposits (particularly in eastern Wisconsin's Door Peninsula and Fox River Valley) is a documented concern. PFAS from industrial and military sources affect multiple communities. Wisconsin's Department of Natural Resources regulates well construction, and the state has conducted extensive well contamination surveys.
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Missouri Well Water Guide
About 30% of Missourians rely on private wells, with the highest rates in the rural Ozarks, agricultural northwest and northeast corners, and Bootheel region. Missouri's Ozark Plateau — one of the largest karst regions in North America — creates a highly permeable groundwater system where bacterial contamination from agricultural and septic sources can reach wells rapidly. The southeast Missouri Bootheel has Delta-style agricultural contamination. PFAS from military sites, naturally occurring radium in some deep aquifers, and industrial contamination in the St. Louis metropolitan area are additional concerns. MDNR regulates well construction.
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Oklahoma Well Water Guide
About 25% of Oklahomans rely on private wells, concentrated in the rural eastern Oklahoma mountains and plains communities outside the reach of municipal water systems. Oklahoma's groundwater contamination concerns include nitrate from agricultural and poultry operations (particularly in the Panhandle and northeastern Oklahoma), naturally occurring radium and uranium in some western Oklahoma aquifers, arsenic from alluvial and geological sources, and oil and gas-related contamination (Oklahoma is a major petroleum state). ODEQ and the Oklahoma Water Resources Board regulate well construction and provide voluntary testing guidance.
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North Dakota Well Water Guide
North Dakota has one of the highest rates of private well use in the nation — about 48% of residents rely on private wells, reflecting the state's vast rural agricultural landscape. North Dakota's groundwater challenges are driven by its geology and land use: naturally occurring arsenic in glacial drift sediments, nitrate and bacterial contamination from livestock and crop agriculture, naturally high sulfate and total dissolved solids from sedimentary geology, and oil and gas contamination in the Bakken oil fields. The ND Department of Environmental Quality regulates well construction.
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South Dakota Well Water Guide
About 45% of South Dakotans rely on private wells — one of the highest rates in the nation — reflecting the state's sparse rural population across vast agricultural and ranch lands. South Dakota's groundwater is shaped by its geology and land use: naturally occurring arsenic in the James River lowlands and glacial drift, nitrate from livestock and crop agriculture, naturally high sulfate and TDS from sedimentary rock, and uranium from the Black Hills' granitic geology. DENR regulates well construction and maintains a private well program.
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Nebraska Well Water Guide
About 40% of Nebraskans rely on private wells, with the highest rates in rural agricultural communities across the state and in the Sandhills region. Nebraska sits atop the High Plains (Ogallala) Aquifer — one of the world's largest groundwater systems — which provides water for both agriculture and domestic wells. The Ogallala's nitrate contamination from decades of fertilizer application is Nebraska's most significant well water challenge. Naturally occurring arsenic in alluvial and loess deposits in the Platte River valley and eastern Nebraska, and uranium from the Niobrara chalk formation in central Nebraska, are additional concerns. NDEE regulates well construction.
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Colorado Well Water Guide
About 25% of Coloradans rely on private wells, primarily in rural agricultural communities on the Eastern Plains, mountain towns without public water systems, and exurban foothills communities. Colorado's varied geology creates distinct regional risks: naturally occurring arsenic and uranium in the Front Range's granitic and volcanic geology, nitrate from the Eastern Plains' agriculture and confined feeding operations, naturally elevated fluoride in some plains aquifer systems, and PFAS from military and industrial sources along the Front Range. CDPHE regulates well construction under the Colorado Water Well Construction Rules.
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Utah Well Water Guide
Only about 12% of Utahns rely on private wells — the state's population is heavily concentrated in the Wasatch Front metropolitan areas served by municipal water. Private well users are primarily in rural agricultural communities in the Uintah Basin, Cache Valley, and remote desert communities. Utah's geology creates specific risks: naturally occurring arsenic from volcanic geology in many parts of the state, uranium from the Colorado Plateau's extensive uranium deposits, and fluoride in some basin-fill aquifer systems. The Utah Division of Water Quality regulates well construction.
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Wyoming Well Water Guide
About 45% of Wyomingites rely on private wells — one of the highest rates in the Mountain West, reflecting Wyoming's vast rural landscape and sparse population. Wyoming's groundwater quality is shaped by its geology and resource extraction: naturally occurring arsenic, uranium, and fluoride from volcanic and sedimentary formations; oil and gas contamination from the state's extensive petroleum industry; and coal bed methane extraction that has affected groundwater in parts of the Powder River Basin. The Wyoming DEQ regulates well construction and maintains a private well program.
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Montana Well Water Guide
About 48% of Montanans rely on private wells — one of the highest rates in the nation — reflecting the state's vast rural landscape. Montana's groundwater quality is shaped by its geology: naturally occurring arsenic from volcanic and hydrothermal geology is the most pervasive concern, affecting wells in the Clark Fork watershed, Butte area, and numerous other regions. Historic hard rock mining — particularly copper mining around Butte — has created some of the nation's most contaminated groundwater. Uranium from granite and sedimentary geology, and nitrate from agricultural areas in the eastern plains, are additional concerns. MDEQ regulates well construction.
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Idaho Well Water Guide
About 40% of Idahoans rely on private wells — roughly 680,000 people — with the highest rates in rural agricultural communities in the Snake River Plain, mountain communities, and the northern Idaho Panhandle. Idaho's groundwater quality reflects its volcanic geology and agricultural intensity: naturally occurring arsenic from the Snake River Plain's basaltic and rhyolitic geology, nitrate from the Magic Valley's intensive dairy and potato farming, PFAS from Mountain Home AFB and other sources, and naturally high levels of iron and manganese in basalt aquifer systems. IDWR and DEQ jointly regulate well construction and water quality.
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Hawaii Well Water Guide
About 18% of Hawaiians use private wells, primarily on the Big Island's rural communities, parts of Maui and Oahu outside municipal service areas, and agricultural properties. Hawaii's unique volcanic geology creates a distinctive groundwater picture: the primary aquifer systems are young basaltic lava flows that act as highly permeable conduits. Agricultural contamination from former sugar and pineapple plantations — particularly DBCP (dibromochloropropane) and EDB (ethylene dibromide) from pineapple production — is a legacy contamination issue. Naturally elevated iron and manganese in basalt aquifers, and PFAS from Pearl Harbor/Hickam AFB, are additional concerns. DOH regulates well construction.
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Alaska Well Water Guide
About 45% of Alaskans rely on private wells or other small water systems — one of the highest rates in the nation — given the state's vast rural communities without municipal infrastructure. Alaska's remote geography creates unique groundwater challenges: naturally occurring arsenic from volcanic and hydrothermal geology (particularly in the Ring of Fire corridor), naturally elevated iron and manganese from glacial and alluvial deposits, PFAS from military installations (multiple Air Force bases), and emerging concerns about permafrost thaw affecting shallow water systems. DEC regulates well construction and provides testing guidance.
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Well water guides for additional states will be added as coverage expands in Phase 2.
Official EPA Well Water Resources
The EPA's Private Wells program is the authoritative federal resource for well owners. It includes guidance on testing, treatment, and finding certified labs.
EPA Private Wells Program