Nitrate in Coastal South Carolina Well Water: A 2026 County Risk Guide for Private Well Owners

Nitrate is the contaminant most likely to exceed the EPA's Maximum Contaminant Level in US private wells, with USGS NAWQA data showing approximately 7 percent of sampled domestic wells exceeded the federal limit of 10 mg/L (as nitrogen) in national surveys. For coastal South Carolina private well owners, the risk is not uniform: it tracks agricultural land use and well depth. Shallow wells in Horry County farming areas face meaningfully higher exposure than deep Floridan aquifer wells in Beaufort County. This guide maps that variation county by county across the 7 counties where Solomon Home Water Solutions serves private well customers, explains where the risk is highest and why, and describes which certified treatment methods actually remove nitrate. If you are on a private well in coastal SC, this is the data you need before your next test.

What is nitrate and why does it matter in drinking water?

Nitrate (NO3) is a naturally occurring ion that forms when nitrogen compounds in soil or water oxidize. It is also introduced into groundwater through synthetic fertilizers, animal waste, and septic system discharge. Unlike many contaminants, nitrate dissolves readily in water and travels quickly through sandy or permeable soils into shallow aquifers. It does not bind to soil particles the way heavy metals do, which makes it one of the most mobile groundwater contaminants in agricultural areas.

The EPA set the nitrate MCL at 10 mg/L (as nitrogen) specifically to protect infants under 6 months from methemoglobinemia, a condition in which nitrate converts to nitrite in the infant gut, reacts with hemoglobin, and reduces the blood's capacity to carry oxygen. Symptoms range from a bluish skin tone to respiratory distress. The condition is rare but serious, and the MCL is calculated to eliminate that risk at typical infant formula preparation volumes.

For adults, nitrate at levels near or modestly above the MCL is generally not an acute health concern. However, the World Health Organization has noted that some epidemiological studies link longer-term exposure to nitrate above 11 mg/L to modestly elevated risk for certain gastrointestinal cancers. That evidence is still being evaluated, but it is a reason to treat a well at 10 to 14 mg/L rather than wait for higher readings, particularly for households where the well is the primary drinking water source.

Public water systems in South Carolina must test regularly and report results in their annual Consumer Confidence Reports. Private well owners have no such safety net. The SC Department of Environmental Services recommends annual testing for nitrate as part of a minimum private well panel, plus retesting within 72 hours after any flooding event that reached the wellhead.

How nitrate reaches private wells in coastal South Carolina

Nitrate contamination of groundwater follows a predictable path: nitrogen-rich inputs at the surface, a permeable pathway through the soil, and a shallow water table or unconfined aquifer that captures the leachate. In coastal South Carolina, three nitrogen sources dominate:

• Synthetic fertilizers on row crops: Horry County is one of South Carolina's leading tobacco and soybean producers. Tobacco in particular receives heavy nitrogen applications. When rainfall exceeds crop uptake, excess nitrate percolates through the sandy loam soils of the Coastal Plain into shallow surficial aquifer wells.
• Poultry litter: Berkeley County has a significant poultry operation presence in its outlying areas. Poultry litter applied to fields as fertilizer is a concentrated nitrogen source. USGS studies of agricultural watersheds with high poultry density consistently document elevated nitrate in shallow groundwater.
• Septic systems: In suburban-fringe areas with high septic density and shallow water tables, nitrogen from wastewater can reach groundwater. This is less of an acute risk than row crop fertilizer in most coastal SC settings, but it matters for transitional areas like parts of Dorchester and Berkeley counties.

The key protective factor is aquifer depth and confinement. The deep confined Floridan, Black Creek, and Middendorf aquifers that supply many coastal SC private wells are insulated from surface nitrogen by thick confining clay layers. USGS NAWQA data from principal aquifer studies consistently shows that nitrate concentrations in deep confined aquifer samples are far lower than in surficial or water-table aquifer samples. Depth is the primary natural protection a private well can have against nitrate.

County-by-county nitrate risk for private wells across Solomon's service area

The table below synthesizes USDA NASS South Carolina agricultural census data, USGS NAWQA aquifer vulnerability assessments for the SC Coastal Plain, and SCDES private well testing guidance into a county-level reference for the 7 counties within Solomon's service territory. Risk ratings reflect the relative probability that a typical shallow private well in rural portions of that county would encounter elevated nitrate. Deep confined aquifer wells have substantially lower risk regardless of county.

Which wells face the highest exposure risk?

Across Solomon's service counties, three specific well-and-setting combinations carry the most meaningful nitrate risk:

1. Shallow surficial aquifer wells in Horry County farming areas. Horry is South Carolina's top tobacco-producing county. Shallow wells within a quarter mile of active crop fields can show elevated nitrate when spring planting fertilizer applications coincide with seasonal rainfall. These wells often draw from as little as 30 to 80 feet, with minimal clay protection.
2. Rural Berkeley County wells near poultry operations. Poultry litter contains 25 to 55 pounds of nitrogen per ton, much of it as organic nitrogen that rapidly converts to nitrate in soil and groundwater. Berkeley's rural northwestern areas have documented poultry farm density that translates to higher background nitrate in shallow wells.
3. Older wells with damaged casings in any county. A well with a cracked or corroded casing, a loose well cap, or inadequate grout in the annular space can allow surface water to short-circuit even a deep, otherwise-protected aquifer. SCDES well permitting data shows a significant fraction of older coastal SC wells were constructed before modern casing standards. Any well older than 25 years should have its casing inspected along with routine nitrate testing.

How to test your private well for nitrate

Nitrate testing in South Carolina must be done by a state-certified laboratory to produce legally defensible results. The SC Department of Environmental Services maintains a list of certified labs at scdes.sc.gov. Basic nitrate-only testing is affordable at a certified lab. A comprehensive well panel that includes bacteria, pH, iron, manganese, hardness, and nitrate costs more but gives a full baseline picture.

Timing matters for nitrate tests. Spring samples collected after planting and fertilizer application tend to capture peak nitrate levels. A test taken in mid-winter during dormancy may underestimate the peak seasonal exposure. If you test in winter and results are below 5 mg/L, a follow-up spring test in a subsequent year is advisable before concluding nitrate is not a concern for your well.

Point-of-use nitrate test strips are available at hardware stores but are not accurate enough for health decisions. Use a certified lab for any result that will inform treatment choices or real estate transactions.

What to do if your nitrate result exceeds 10 mg/L

If a certified lab result shows nitrate above the EPA MCL of 10 mg/L as nitrogen, three treatment options are proven effective:

Reverse osmosis is the most practical choice for most households. It does not generate a significant waste stream in the way whole-house ion exchange does, it requires no regeneration chemicals, and it handles a wide range of other contaminants (arsenic, fluoride, PFAS, lead) simultaneously. Solomon installs reverse osmosis systems sized for the kitchen drinking and cooking circuit, which is where infant formula and most drinking water is consumed. Most households with a nitrate problem do not need whole-house treatment; they need protected drinking water.

What does not remove nitrate: Standard activated carbon filters, ceramic filters, sediment filters, UV disinfection systems, and cation-exchange water softeners do not reduce nitrate. Using one of these as a nitrate solution is a common and dangerous mistake.

One additional step worth considering: after treatment, retest the treated water annually to confirm the system is performing as expected. RO membranes degrade over time, and a compromised membrane may show reduced nitrate rejection before it shows obvious signs of failure.

For households with a nitrate result between 5 and 10 mg/L, no immediate regulatory action is required, but the trend matters. If results are rising year over year, the source is likely growing (new nearby land use, casing deterioration, water table change). Treat the trend as a signal to act before the MCL is exceeded rather than after.

Additional reading: Solomon's guides on bacteria risk in coastal SC private wells, SCDES private well testing rules in SC, and fluoride and radium in Black Creek and Middendorf aquifer wells cover additional water quality parameters that matter for coastal SC well owners.