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Last reviewed 2026-10-16

Johnston Co. Well Water Testing

If the tub in a Smithfield or Benson farmhouse is ringed with orange, the well is the usual suspect. NC DHHS State Laboratory results for 1998-2010 show iron above EPA's 0.3 mg/L secondary limit in 476 of 1,458 Johnston County wells, or 32.65%, the highest iron share of the three North Carolina counties on this site.

USGS estimated that 46,270 people in the county, about 24.9% of residents, relied on a private well in 2015. Johnston Environmental Health sells the state-lab tests that tell an installer what to build: its July 1, 2026 fee schedule lists total coliform at $29 and a full inorganic panel at $74.

Permits

Step 1: Pick up bottles from Johnston County Environmental Health, 309 E. Market Street, Smithfield (919-989-5180), and collect the sample yourself; the county fee schedule adds $30 per visit if staff do the sampling.

Step 2: For staining or odor, order the full inorganic panel ($74) and, if the water smells of rotten eggs or leaves slime in the toilet tank, the iron bacteria ($34) or sulfur-reducing bacteria ($45) tests the same schedule lists.

Step 3: For a family with an infant, add nitrates/nitrites ($32 on the county schedule); arsenic speciation is listed at $31 for the rare well that tests high.

Step 4: Repairs to the well itself carry no county permit charge under the Johnston fee schedule, while the fee schedule lists a new private well permit at $400; G.S. 87-97 requires new wells to be inspected and sampled before use.

Step 5: After a filter or neutralizer goes in, send a second inorganic sample so the iron and pH numbers are confirmed by the state lab rather than a dealer's strip test.

Local conditions

Johnston sits across the fall line. Northwest of Clayton and Archer Lodge, wells reach crystalline Piedmont bedrock; toward Smithfield, Four Oaks and Benson they draw from Coastal Plain sand and clay aquifers in the southeast half of the county, where dissolved iron is common.

Manganese travels with the iron: NC DHHS data show 425 of 1,460 Johnston wells (29.11%) above the secondary limit, which shows up as black specks and dark stains.

Acidity is the other half of the story. The DHHS record puts 564 of 1,463 samples (38.55%) below pH 6.5, with a county average of 6.60. Acidic water can dissolve copper pipe, and copper was above 1.3 mg/L in 16 of 1,461 wells in that record.

Health-limit metals are less common here than in the Piedmont counties. UNC's NCWELL tables for 1998-2019 show arsenic above EPA's standard in 24 of 2,003 wells (1.2%), lead above 15 micrograms per liter in 50 of 2,003 (2.5%) and nitrate above the federal limit in 13 of 558 (2.33%).

What drives local prices

  • Iron level and pH together decide the filter. HomeGuide's published installed ranges run $1,000-$3,500 for an iron or manganese filter and $800-$2,500 for a calcite neutralizer, and its Birm filter range of $400-$1,200 only applies when the pH is high enough for that media.
  • A softener ($1,200-$3,800 per HomeGuide) helps with modest iron but is a poor fit for acidic water unless a neutralizer sits ahead of it.
  • Media changes add ongoing cost: HomeGuide lists iron filter media replacement at $200-$600 per change, more often on high-iron county wells.
  • Bacteria tests matter here: a $34 iron bacteria or $45 sulfur bacteria result from the county lab can point to shock chlorination before any equipment is bought.

Common jobs

  • Neutralizer plus air-injection iron filter on low-pH Coastal Plain wells
  • Manganese removal for black staining in laundry and fixtures
  • Shock chlorination and retest after an iron-bacteria result
  • Softener added after iron and pH are corrected
  • Whole-house sediment prefilter on sandy wells

Service area

Well households spread along I-95 between Selma and Four Oaks, along US 70 east toward Princeton and Pine Level, and down NC 42 and NC 210 between Clayton, Cleveland and McGee's Crossroads.

The I-40 corridor toward Benson and Meadow has some of the fastest new-home growth on private wells.

Communities: Smithfield, Clayton, Selma, Benson, Four Oaks, Kenly, Princeton, Pine Level, Wilson's Mills, Micro, Archer Lodge, Cleveland

If it is an emergency

Orange water right after heavy rain or new well work is usually sediment and iron, not an emergency. A positive coliform test is different: disinfect, retest through Johnston County Environmental Health, and use bottled water until it clears.

Questions about Johnston County

What does Johnston County charge for a well water test?

The July 1, 2026 county fee schedule lists total coliform at $29, a full inorganic panel at $74 and nitrates/nitrites at $32 when you collect the sample. Staff sampling is $30 per visit.

Why is Johnston County well water orange or black?

Iron makes orange stains and manganese makes black ones. NC DHHS data show about a third of tested county wells above the iron limit and 29% above the manganese limit.

Is my Johnston County well water acidic?

Possibly. 38.55% of 1,463 samples in the DHHS record were below pH 6.5. A neutralizer is usually installed before the iron filter in that case.

Should I test for iron bacteria?

If you see red-brown slime in the toilet tank or the water smells musty, yes. The county lists the iron bacteria test at $34 and sulfur-reducing bacteria at $45.

Is arsenic common in Johnston County?

Not very. UNC's NCWELL tables show 1.2% of 2,003 tested wells above EPA's arsenic standard, far below the rate in Union County.

Sources

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