Groundwater in North Carolina

North Carolina has the fourth highest number of private well users in the country.15 While more than 3 million North Carolinians rely on groundwater as their primary drinking water source, fewer than 200,000 wells in our state were tested for contaminants in the last decade (2000-2010).62

The North Carolina Division of Public Health recommends testing well water every year for coliform bacteria, every two years for heavy metals, nitrates, nitrites, lead, copper, and volatile organic compounds, and every 5 years for pesticides.
Since 2008, all newly constructed drinking water wells in North Carolina must be tested for bacterial and chemical contaminants within 30 days of the well completion; however, there are no other required tests for private wells in North Carolina.

What is groundwater?

Groundwater is water that is found under the earth’s surface “between rocks and soils”.56 Groundwater begins as rain and snowmelt that seeps through plant roots, soil, and rocks and eventually collects in the crevices of rocks and hollow spaces underground. Groundwater eventually returns to the land surface and flows to streams, rivers, lakes, and oceans where it can evaporate and again fall to the earth as rain or snow. The cycle of evaporation, condensation, precipitation- and the movement of groundwater- can take many years.

Potential sources of groundwater contamination

A majority of private well water used for drinking comes from groundwater. All water, even water from deep underground, contains some impurities. Impurities are contaminants or pollutants that can enter groundwater from natural as well as anthropogenic (human) and animal sources.7 Contaminants can enter groundwater through the erosion of natural mineral deposits, precipitation (rainfall or snowfall), and run-off.  Contaminants can also be released by agricultural and industrial activities. Drinking water supplies can be impacted by activities that occur close to the drinking water source, as well as some activities that occur many miles away. Examples of potential sources of groundwater contamination:

  • Improperly sealed well pipes or nearby abandoned wells5
  • Run-off from roadways, parking lots, and paved areas
  • Gasoline and chemical spills
  • Sewage, untreated wastewater, leaking septic tanks
  • Leaking underground storage tanks
  • Landfills and old dump sites, unlined waste impoundments
  • Hazardous waste sites
  • Airborne emissions and waste disposal from factories, petroleum refineries, metal smelters, and power plants
  • Mine and drilling sites
  • Agricultural run-off (fertilizers, pesticides)
  • Run-off from livestock operations57
Some drinking water contaminants are harmful to human health but do not cause any noticeable changes to the taste, smell, or color of the water.54 The absence of any unpleasant changes to the water means that if the drinking water is not regularly tested, it may be contaminated for many years before the problem is discovered.

Additional information about groundwater


Private wells

Private wells are constructed to capture water that is underground to be used for drinking and other purposes such as irrigation.  Wells typically consist of a pipe that connects an aboveground cap, or wellhead, to an aquifer. An aquifer is an underground formation that contains water. The well is attached to a pump that draws the water from the aquifer and delivers it to a house or faucet. Wells can be constructed in a variety of ways, including dug, driven, or drilled, depending upon the underlying geology of the land, the depth of the aquifer, and the available resources of the well driller.5 At present, few wells are hand dug; most are drilled by a truck-mounted drill rig.51 Wells can vary in depth from only a few feet where the water table is very shallow, to many feet where the water table is deep.

Common well terminology

Aquifer- An underground formation or group of formations in rocks and soils containing enough ground water to supply wells and springs.5 Water table- The top of the saturated soil or rock in an aquifer.  When the aquifer recharges, the water table rises, then gradually drops as the water is removed or used.5 Well casing– The tubular lining of a well. Also a steel or plastic pipe installed during construction to prevent collapse of the well hole.5 Wellhead/well cap – The top of a structure built over a well. Wellheads are important for preventing contaminants on the surface from entering underground water supplies and preventing items or animals from falling into the well tube.5

Additional information about private wells


Well maintenance

The NC Department of Health and Human Services recommends testing your well water every year for coliform bacteria, every two years for heavy metals, nitrates, nitrites, lead, copper, and volatile organic compounds, and every 5 years for pesticides.
More frequent testing is recommended if you suspect contamination or if there is a hazardous spill in your area.

When to test your well water

All newly constructed private wells in North Carolina must be tested by the North Carolina State Laboratory of Public Health or a certified laboratory prior to establishing the well as a source of drinking water. Well water should also be tested after repairs or replacements to any of the well components and after flooding events since contaminants can enter your well when it is opened or if the wellhead is underwater. According to the US Centers for Disease Control and Prevention (CDC), well owners should also perform a physical assessment of the wellhead and casing once a year to make sure there are no mechanical or structural problems that could introduce contaminants. You should also have your well tested if:

  1. There are known problems with well water in your area,
  2. You have experienced problems near your well (i.e., flooding, land disturbances, and nearby waste disposal sites),
  3. You replace or repair any part of your well system,
  4. You notice a change in water quality (i.e., taste, color, odor).60

There are guidelines for collecting water samples of well water in order to prevent cross-contamination and to preserve the sample for laboratory analysis. Find out more about how to test your well water or contact your local health department for more information about how to sample your well water.

How to identify possible contaminants and common well problems

Some contaminants in drinking water can cause changes to the appearance, taste, or smell of water. Some water quality issues may also be noticeable because they cause illness or damage household plumbing and appliances. Other contaminants may not cause any noticeable changes to your water, but they may still be present in levels that are unsafe to drink. The US Environmental Protection Agency (US EPA) recommends testing private drinking water supplies regularly to identify contamination problems early and avoid long-term health effects or damage to your plumbing or well components.7 The US EPA also advises all well owners to be aware of activities in the nearby watershed that may affect the quality of the water in your drinking well. Below is a chart of common reasons to test your well water.


How to test your well water

Routine testing of well water is important for monitoring the quality and safety of household drinking water.  Routine testing can help well owners diagnose well issues in need of repair and identify potential contamination early.

Sampling procedure To receive a chemical analysis from the NC State Laboratory of Public Health (NC SLPH), private well owners must submit a water sample to a county health department.  Sampling containers, which are required for all tests performed by the NC SLPH, can be obtained from the health department.  The county health department will arrange delivery of the sample to the State Laboratory for analysis or, in some counties, may visit your home to perform the sample collection.  The NC Division of Public Health or your local health department will mail or email your results to you within several weeks of submitting the water sample.

Sample collection guidelines

  • Use the test kit and sampling containers provided by your local health department.
  • Appropriately disinfect or flush the pipes prior to collecting a sample.
    • For some tests it is recommended that well owners allow water to flow from the faucet for several minutes before collecting a water sample. This will flush all stagnant water that has been sitting in the pipes. Well owners may also be encouraged to disinfect the faucet before collecting a sample.
    • Contaminants such as lead and copper, the State Laboratory may recommend taking an initial sample when you turn on the faucet and an additional sample after allowing the water to run for 15 minutes. They may also recommend sampling at an indoor faucet as well as at the wellhead to help determine whether the contamination is caused by the pipes or another source.
  • Fill the sampling container to the brim or until the water is in contact with the container lid. Avoiding extra air in the container will also help to avoid contamination.
  • Store the sample at the temperature indicated on the sampling instructions.
  • Label all containers and identify which water analyses you would like performed.
  • Check to ensure that the lid is properly secured before transport.
  • Mail the sample or deliver to your local health department as soon as possible.

Proper sampling procedures will ensure the quality and accuracy of your well water sample. Proper sampling techniques also help the laboratory to detect very low levels of contaminants in your water and to correctly identify the contaminants.  If you suspect the sample was contaminated during collection, re-submit a well water sample.  The NC SLPH may also recommend re-submitting a well sample if contaminants of concern are discovered. For more information about submitting a water sample for analysis, visit the Environmental Sciences section of the NC State Laboratory of Public Health.

Sampling information from the NC State Laboratory

How to collect a sample for bacterial analysis. How to collect a sample for inorganic analysis. The following inorganic contaminants are tested by the NC State Laboratory of Public Health: Acidity, alkalinity, aluminum, amphibole, antimony, arsenic, asbestos, barium, beryllium, bromate,  bromide, cadmium, calcium, chloride, chlorite, chromium, chrysotile, color, conductivity, copper, cyanide, dissolved organic carbon (DOC), fluoride,  hardness, iron, lead, magnesium, manganese, mercury, nickel, nitrate, nitrite, orthophosphate, pH, selenium, silica, silver, sodium, sulfate, temperature, thallium, total dissolved solids (TDS), total organic carbon, UV absorbance, and zinc. How to collect a sample for organic analysis. The following organic contaminants are tested by the NC State Laboratory of Public Health: 1,1,1-trichloroethane, 1,1,2- trichloroethane, 1,2- dichloroethane, 1,2,4-trichlorobenzene, 1,2-dibromo-3-chloropropane, 1,2-dichloroethylene, 1,2-dichloropropane, 1,4- dichlorobenzene, 2,4,5-tp, alachlor, atrazine, benzene, benzo(a)pyrene, bromodichloromethane, bromoform, carbofuran, carbon tetrachloride, chlordane, chlorobenzene, chlorodibromomethane, chloroform, cis- 1,2-dichloroethylene, dalapon, di-2(ethylhexyl) phthalate, di-2(ethylhexyl)adipate, dibromoacetic acid, dichloracetic acid, dichloromethane, dinoseb, dioxin, diquat, endothall, endrin, ethylbenzene, ethylene dibromide, glyphosate, heptachlor, heptachlor epoxide, hexachlorobenzene, hexachlorocychlopentadiene, lindane, methoxychlor, monobromoacetic acid, monochloroacetic acid, oxamyl, pentrachlorophenol, picloram, polychlorinated biphenyls pcb, simazine, styrene, tetrachloroethylene, toluene, total haloacetic acids, total trihalomethanes, total xylenes, toxaphene, trans- 1,2,- dichloroethylene, trichloroacetic acid, trichloroethylene, and vinyl chloride.

Water testing laboratories in NC

All drinking water analyses must be performed by the NC State Laboratory of Public Health (NC SLPH) or other state-certified laboratory. View all state-certified laboratories.


This project was funded by an ARRA supplement from the National Institute of Environmental Health Sciences (#P42ES005948) 2009-2011.