Well water testing in Merrimack County, New Hampshire

Last verified: 2026-11-01 · 12 sources · What we couldn't verify

Arsenic is the headline risk: USGS ranks Merrimack among the four New Hampshire counties most likely to have bedrock-well arsenic above 5 and 10 µg/L, and 44% of historical Bow well tests were over 10 ppb. The state lab is in Concord and charges $95 for its Standard Analysis ($120 with radon); NHDES offers free PFAS sampling for prioritized wells.

NHDES says private wells are the main source of drinking water for about 46% of New Hampshire's population (about 520,000 people). There is no statewide testing requirement, but some towns require testing before a certificate of occupancy; a 2021 NHDES presentation listed Bow (Merrimack County) among them. Check with your town for current rules.^[2]

Free and low-cost testing programs

Labs that serve the county

NHDES's lab list was last updated 9/20/2024. Accreditation is per test, so confirm with NHDES's Accredited Laboratory Search (NHELAP: (603) 271-2998 / (603) 271-5314, nhelap@des.nh.gov) that a lab is accredited for every test you need.^[1]

Local contaminants of concern

• Major concern Arsenic. A USGS/NH statewide model found that Merrimack, Strafford, Hillsborough and Rockingham Counties have the greatest potential for bedrock-well arsenic above 5 and 10 µg/L. In Bow, a 2018 town summary of 201 historical residential well tests found 44% above 10 ppb (the EPA standard) and 57% above 5 ppb, with a maximum of 176 ppb. Statewide, 25% of wells tested at the state lab (2006 - Aug 2020) exceeded 5 µg/L.^[10][12][2]
• Major concern Radon in water. Statewide, 30% of wells tested at the state lab exceeded the 2,000 pCi/L radon testing advisory. Bow's town website says local geology makes radon more likely. We did not find a reliable Merrimack County rate.^[2][11]
• Moderate concern Uranium. In Bow's 2018 summary, 8% of 154 well tests exceeded the 30 ppb uranium standard (median 11 ppb). Statewide, 4% of wells tested at the state lab exceeded 30 µg/L.^[12][2]
• Moderate concern Lead and copper (plumbing). Statewide first-draw (stagnant) samples: 13% exceeded 0.015 mg/L lead and 12% exceeded 1.3 mg/L copper (2% and 1% after flushing). In Bow, 8% of 154 stagnant samples were over 15 ppb lead and 23% over 5 ppb.^[2][12]
• Moderate concern Sodium and chloride (road salt). Statewide, 34% of wells tested at the state lab exceeded 20 mg/L sodium and 3% exceeded 250 mg/L chloride.^[2]
• Moderate concern Iron and manganese. Statewide, 17% of wells tested at the state lab exceeded 0.3 mg/L iron and 5% exceeded 0.30 mg/L manganese.^[2]
• Not verified PFAS (PFOA, PFOS, PFHxS, PFNA). NHDES says PFAS have affected private wells throughout New Hampshire, especially in the south, and recommends every well owner test for PFOA, PFOS, PFHxS and PFNA. We did not find Merrimack County-specific PFAS well results.^[5][1]
• Lower concern Nitrate / nitrite and bacteria. Statewide, essentially no wells tested at the state lab exceeded 10 mg/L nitrate (0%) or 1 mg/L nitrite. No county bacteria rate was in our sources; NHDES still recommends testing bacteria, nitrate and nitrite every year.^[2][1]

The USGS finding is a probability model, not a test of any single well. The Bow figures are historical tests compiled by the town (2018 flier), and the statewide figures are wells whose owners chose to test at the state lab (2006 - Aug 2020); both can skew toward problem wells. A Merrimack-only breakdown of state lab data is on the NH DHHS Private Well Water Quality Dashboard, which we could not read automatically.

A county rate can't tell you what's in your well. Only a test can. See what to test for.

Typical cost

Prices are from the published lists cited, as of the last-verified date. Confirm before ordering.

How often to test

• Every year: bacteria (total coliform and E. coli), nitrate and nitrite.^[1]
• Every 3-5 years: arsenic, chloride, copper and lead (stagnant and flushed), fluoride, hardness, iron, manganese, pH, radon, sodium, uranium, and PFAS (PFHxS, PFNA, PFOA, PFOS).^[1]
• PFAS: if a first test finds none and budget is tight, NHDES says waiting longer is acceptable if nearby land use does not change.^[1]
• Home buyers: test before buying if the seller has no recent test. After installing treatment: test treated water, then every 3-5 years.^[1]

How to collect a sample

Steps from the NH state lab's Standard Analysis kit (private labs have their own instructions):

1. If you recently disinfected the well, make sure all chlorine is gone. Use a clean indoor cold-water faucet that does not leak; do not touch the inside of bottles or caps.
2. Let water sit in the pipes at least 6 hours (overnight is best), then immediately fill the small "First Draw for Lead/Copper" bottle.
3. Remove the aerator if possible, clean the faucet rim with dilute bleach (1 capful per cup of water), and run the water for 1 minute.
4. At a gentle stream, fill the sterile bacteria, nitrate/nitrite and non-sterile bottles. For radon, slowly fill the glass vial to a crown, cap it, and check upside down for bubbles (refill if any).
5. Keep samples cold (not frozen) and deliver ASAP: bacteria within 30 hours, radon and nitrate/nitrite within 48 hours. Samples arriving above 35°C (95°F) are rejected.

Source^[3]. General steps: How to test your well water.

After you get results

Enter your results into NHDES's Be Well Informed web tool for health information and the treatment type that addresses each result. If PFAS is over a standard, the NHDES rebate above can cover up to $5,000 of treatment.^[1][6]

What we couldn't verify

• Merrimack County breakdowns of state lab data (arsenic, radon, uranium rates): the NH DHHS Private Well Water Quality Dashboard blocks automated access.
• A reliable Bow or county radon-in-water rate: the 2018 Bow flier's radon row is internally inconsistent (median 6,900 pCi/L but only 20% of samples listed above 2,000), so we did not use it.
• Eastern Analytical (now Eurofins) prices, kit ordering, mail-in policy and current residential intake; its website now redirects to Eurofins' general site and its residential order form no longer loads.
• Nelson Analytical's mail-in policy, Canterbury drop box hours, and which of its two online price lists is current (we show the kit order-form prices).
• Granite State Analytical's Tilton drop-off: NHDES's list mentions Tilton, but the lab's own drop-off page no longer lists it.
• Whether Bow still requires well testing for a certificate of occupancy (the source is a 2021 NHDES presentation), which lab and price Bow's Town Clerk kits use, and whether the town's Test your Well days still run.
• PFAS results for Merrimack County private wells (the NHDES PFAS Sampling Dashboard is interactive and we could not read it).
• The number or share of Merrimack County residents on private wells.
• Any Concord or other municipal well-testing help in the county besides Bow; we found none.

Sources

1. NH Department of Environmental Services: Water Testing Guidance for Private Well Users (April 2026; lab list updated 9/20/2024)
2. B. Kernen, NHDES (hosted by City of Portsmouth): Private Wells in Portsmouth (presentation, Sept. 1, 2021; EPHT combined NHDES/NH PHL data 2006 - Aug 2020)
3. NH DHHS Public Health Laboratories: Water Test Submittal Form & Water Testing Guide / Sample Collection Instructions
4. NH DHHS: Water Analysis Laboratory Program
5. NHDES PFAS Response: Private Wells (PFAS testing)
6. NHDES PFAS Response: PFAS Removal Rebate Program for Private Wells
7. Granite State Analytical: Residential Services (test packages and prices)
8. Granite State Analytical: Drop-Off Locations
9. Nelson Analytical Lab: Request Sample Test Kits (price list and lab locations) (site currently shows a browser security warning: its certificate expired in July 2025)
10. U.S. Geological Survey: Estimated Probability of Arsenic in Groundwater from Bedrock Aquifers in New Hampshire, 2011 (Scientific Investigations Report 2012-5156)
11. Town of Bow: Private Well Owners
12. Town of Bow Drinking Water Protection Committee: Arsenic, Lead and Radon - Most Common Well Water Contaminants in Bow (2018 flier)

All sources accessed on or before 2026-11-01.

More useful links

• NHDES private wells page (links to the Be Well Informed tool)
• NHDES PFAS Sampling Dashboard

Other New Hampshire counties

• Hillsborough County
• Rockingham County

All New Hampshire county guides