Well water in Merrimack County, New Hampshire
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Testing strongly recommended
private wells tested between 2006 and 2020 in Merrimack County had arsenic above the New Hampshire guidance level (5 ug/L), according to NH DHHS.
4,953 private wells tested 2006 to 2020 in state summaries; 3,880 test results across 17 contaminants from at least 451 wells, 1966 to 2022; nitrate has the most at 564. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
NHDES samples private wells near known or suspected PFAS sources (industrial sites, airports, landfills, fire training areas), and wells with a detection are resampled over time. PFAS shares describe wells that were tested for a reason, not every well in the area.
An estimated 47,542 people in Merrimack County get their drinking water from a private well, per NH DHHS WISDOM, BRFSS 2020. That is about 47% of residents (survey range 41% to 53%).
Separately, the USGS national arsenic model estimates that 11% of the 63,556 people on private wells in Merrimack County draw water above 10 ug/L (the model's range is 8% to 16%), from geology and well depth rather than local tests.
What homeowner tests found
NH DHHS WISDOM private well summaries: private wells tested and reported to the state, 2006 to 2020. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA. County and state figures combine the town summaries, weighted by wells tested; medians are not combined.
| Contaminant | Above state level | Wells tested | Median | 95th pct | Highest | State level |
|---|---|---|---|---|---|---|
| Radon | 2,140 | 330,000 | 2,000 pCi/L | |||
| Arsenic | 4,603 | 1,040 | 5 ug/L | |||
| Sodium | 4,194 | 2,186 | 20 mg/L | |||
| Iron | 4,212 | 74,200 | 300 ug/L | |||
| Lead (stagnant) | 3,868 | 2,490 | 15 ug/L | |||
| Copper (stagnant) | 3,853 | 14.2 | 1.3 mg/L | |||
| Manganese | 4,208 | 43,300 | 300 ug/L | |||
| Uranium | 4,248 | 3,340 | 30 ug/L | |||
| Chloride | 4,897 | 3,300 | 250 mg/L | |||
| Nitrate | 4,875 | 21 | 10 mg/L | |||
| Fluoride | 4,953 | 7.6 | 4 mg/L | |||
| Nitrite | 4,873 | 0.5 | 1 mg/L |
What individual samples found
Each row summarizes every public sample for that contaminant inside Merrimack County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Above limit | Samples | Detected | Median | Highest | Limit |
|---|---|---|---|---|---|---|
| Arsenic 1986 to 2022 | 206 | 61% | 0.65 | 300 | 10 ug/L EPA limit | |
| Radium (226 + 228) 1987 to 2019 | 24 | 71% | 0 | 18.3 | 5 pCi/L EPA limit | |
| Lead 1966 to 2022 | 146 | 58% | 0.09 | 51 | 15 ug/L EPA limit | |
| Uranium 1990 to 2022 | 111 | 67% | 0.044 | 135 | 30 ug/L EPA limit | |
| Copper 1966 to 2022 | 135 | 81% | 0.005 | 7 | 1.3 mg/L EPA limit | |
| Nitrate 1966 to 2022 | 564 | 40% | 0 | 24.5 | 10 mg/L EPA limit | |
| Fluoride 1966 to 2022 | 497 | 85% | 0.3 | 5 | 4 mg/L EPA limit | |
| E. coli 2011 to 2019 | 22 | 0% | 0 | 0 | 0 MPN/100mL EPA limit | |
| Manganese 1966 to 2022 | no limit | 542 | 70% | 40 | 3,700 | 300 ug/L health guideline |
| Chloride 1966 to 2022 | no limit | 537 | 65% | 2 | 435 | 250 mg/L nuisance level |
| Iron 1966 to 2022 | no limit | 502 | 78% | 125 | 84,000 | 300 ug/L nuisance level |
| Sodium 1966 to 2022 | no limit | 460 | 92% | 9 | 184 | 20 mg/L health guideline |
| Radon 1986 to 2003 | no limit | 105 | 99% | 4,900 | 910,000 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: PFOS (9), PFOA (8), PFNA (6), PFHxS (6).
Over time
Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.
| Contaminant | before 2000 | 2000s | 2010s | 2020s |
|---|---|---|---|---|
| Nitrate | <1%483 samples | 0%18 samples | 12%41 samples | 0%22 samples |
| Fluoride | 1%443 samples | n/a | 0%24 samples | 0%21 samples |
| Arsenic | 35%96 samples | n/a | 4%25 samples | 21%76 samples |
| Lead | 3%36 samples | n/a | 0%25 samples | 3%76 samples |
| Copper | 0%25 samples | n/a | 0%25 samples | 3%76 samples |
| Uranium | n/a | n/a | 0%25 samples | 3%76 samples |
Nitrate above the limit in Merrimack County fell from 12% of 41 samples in the 2010s to 0% of 22 in the 2020s.
Arsenic above the limit in Merrimack County rose from 4% of 25 samples in the 2010s to 21% of 76 in the 2020s.
Fluoride, lead, copper, uranium have held within a few points between the two most recent periods with enough samples.
Closer than the county
See the sampled wells near your address
The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.
Check my addressWhat this means
Among homeowners in Merrimack County who sent a sample to the state lab, the health-based limits most often exceeded were arsenic (33% of 4,603 wells), lead (13% of 3,868 wells), and copper (13% of 3,853 wells). These are ordinary wells tested by their owners, so the shares are the best available picture of a typical well here, with one caveat: people test more often when they suspect a problem.
Radon was above the New Hampshire guidance level of 2,000 pCi/L in 56% of 2,140 wells. Radon in water matters because it moves into indoor air during showers and laundry.
Sodium and iron exceed the state's advisory level in a sizable share of wells; these are mostly a taste, staining or diet issue rather than a toxicity one.
What to test for in Merrimack County
- 1Arsenic33% of 4,603 local wells tested were above the New Hampshire guidance level.
- 2Radon56% of 2,140 local wells tested were above the New Hampshire guidance level.
- 3Lead13% of 3,868 local wells tested were above the New Hampshire guidance level.
- 4Copper13% of 3,853 local wells tested were above the New Hampshire guidance level.
- 5Radium (226 + 228)13% of 24 local samples were above the limit.
- 6Uranium6% of 4,248 local wells tested were above the New Hampshire guidance level.
- 7Nitrate1% of 564 local samples were above the limit.
- 8Fluoride1% of 497 local samples were above the limit.
- 9Volatile organic compounds (VOCs)207 leaking underground storage tank sites on record locally.
- 10PFAS41 unlined landfills on record locally.
- 11Metals panel73 hazardous waste sites on record locally.
Test your Merrimack County well for arsenic, radon and lead
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.
Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.
Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.
Where to get a well tested in New Hampshire: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Merrimack County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in Merrimack County
12,289 domestic wells in Merrimack County are on record with the state since 1984. 99% are drilled into bedrock, and the typical well is 345 feet deep (one in ten goes past 600 feet).
In a typical Merrimack County well, bedrock starts about 26 feet down, the median yield is 7.5 gallons per minute, 18% of wells yield under 3 gallons per minute and usually need a storage tank.
Bedrock wells are where arsenic, uranium and radon come from: the water sits in fractures in granite and metamorphic rock and picks up whatever the rock carries. That is why testing for those three matters more here than in a dug or gravel well.
Find your own well's report
The state keeps the driller's report for most wells drilled since 1984. It tells you how deep your well is, where bedrock starts, and how much water it makes, which decides what treatment can work.
- Open NHDES OneStop and choose Water Well.
- Enter your town and one word of your street name. Leave out the house number and the Road or Street part; a short search matches more.
- In the results, click Show for your address to see the report: total depth, depth to bedrock, casing, yield in gallons per minute, static water level, and the driller.
- Save Results exports the whole list to a spreadsheet.
Reports exist only for wells drilled since January 1984, when reporting became mandatory, and street names are as they were when the well was drilled.
The rock under Merrimack County
Not a principal aquifer
The USGS map places this area outside any principal aquifer, which usually means wells here draw from fractured bedrock or thin local deposits rather than a large regional aquifer. Bedrock wells of that kind are where arsenic, radon and uranium turn up, and yields vary from well to well.
Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.
Official help in New Hampshire
Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.
Contamination sources on record in Merrimack County
NHDES records 207 leaking underground storage tank sites, 41 unlined landfills, 73 hazardous waste sites, and 127 reported spills and releases in Merrimack County, among 2,227 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 207
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 41
- unlined landfillsOlder unlined landfills are a leading source of PFAS, VOCs and metals in nearby wells.
- 73
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 127
- reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
- 512
- registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
- 173
- locally identified potential contamination sourcesTowns inventory these (vehicle repair, labs, salt piles, farms) when they draw wellhead protection maps.
- 2
- lined landfills and transfer facilities
- 1,045
- other remediation projects
- 47
- other solid waste facilities
Treatment that fits the local profile
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Lead
Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching
Copper
Neutralizing filter to raise pH; Point-of-use reverse osmosis
Uranium
Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange
Radon
Aeration (bubble-up or diffused) whole-house; Granular activated carbon whole-house (lower levels only)
Radium (226 + 228)
Water softener (cation exchange); Point-of-use reverse osmosis
Systems we would look at first
Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For arsenic
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For arsenic
Whole-house arsenic and uranium filter
whole-house, at the point of entry, about $2,500
Adsorptive iron-based media; sized to your well yield.
For arsenic
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
For lead
Aquasana Claryum 3-Stage under-sink filter
under-sink or countertop, about $175
Certified to NSF/ANSI 53 to reduce 99% of lead and 99.7% of PFOA and PFOS at the tap. Not a fix for arsenic, nitrate or bacteria.
For lead
Acid neutralizing filter
whole-house, at the point of entry, about $1,200
Raises pH so plumbing stops leaching lead and copper.
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Common questions
How deep are wells in Merrimack County?
The typical domestic well in Merrimack County is 345 feet deep, based on 12,289 wells reported to the state since 1984. One in ten is deeper than 600 feet. 99% are drilled into bedrock.
Is there arsenic in well water in Merrimack County?
Arsenic was detected in 61% of 206 public well samples in Merrimack County, and 25% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How high is radon in well water in Merrimack County?
The median radon level across 105 public samples in Merrimack County was 4,900 pCi/L, with a high of 910,000 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Merrimack County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Towns in Merrimack County
- Allenstown0% nitrate
- Andover22% copper
- Boscawen13% copper
- Bow65% arsenic
- Bradford20% arsenic
- Canterbury23% arsenic
- Chichester48% arsenic
- Concord46% arsenic
- Danbury23% copper
- Dunbarton56% arsenic
- Epsom43% arsenic
- Franklin7% copper
- Henniker33% arsenic
- Hill19% lead
- Hooksett27% uranium
- Hopkinton37% arsenic
- Loudon33% arsenic
- Newbury19% lead
- New London31% uranium
- Northfield10% copper
- Pembroke61% arsenic
- Pittsfield38% arsenic
- Salisbury18% arsenic
- Sutton22% copper
- Warner23% arsenic
- Webster32% arsenic
- Wilmot31% arsenic
Counties near Merrimack County
Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.
Want the numbers themselves? Download the New Hampshire dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 3,857 samples in Merrimack County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- NHDES PFAS sampling: 23 samples in Merrimack County. PFAS results for private wells from the New Hampshire Department of Environmental Services Environmental Monitoring Database. Retrieved September 3, 2026.
- NH DHHS WISDOM private well summaries: summaries for 12 contaminants in Merrimack County, up to 4,953 wells each. Town summaries of private well tests run by the New Hampshire Public Health Laboratories, published by NH DHHS through the WISDOM environmental public health tracking portal. Exceedance shares use New Hampshire guidance levels, which are stricter than EPA for arsenic (5 ug/L), manganese (0.3 mg/L), radon (2,000 pCi/L) and sodium (20 mg/L). Statistics for small counts are suppressed (*). Retrieved September 3, 2026.
- USGS national arsenic model (Ayotte 2017): estimated share of 63,556 people on private wells in Merrimack County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.
- NHDES Water Well Inventory: 13,538 well records in Merrimack County, 12,289 domestic. Well construction records reported to the New Hampshire Department of Environmental Services Water Well Board. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 3, 2026.
- NHDES OneStop regulated sites: 2,227 regulated sites located in Merrimack County. Remediation sites, underground storage tanks, solid waste facilities and potential contamination sources from the New Hampshire Department of Environmental Services OneStop database. Retrieved September 3, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.