privatewelldata / States / Massachusetts / Nitrate
Nitrate in well water in Massachusetts
4% of 2,556 sampled wells in Massachusetts had nitrate above the EPA limit of 10 mg/L (as nitrogen) (latest result per well, 12 counties, samples 1944–2023). The highest county share was Nantucket County: 7% of 14 wells. Data updated 2026-10-19.
of sampled wells above 10 mg/L (as nitrogen)
wells with a result
counties with data
counties where 1 in 4+ wells were above
Nitrate in wells most often comes from fertilizer, manure and septic systems, so shallow wells near fields or septic fields are more exposed, and levels can change with the seasons. Only a lab test shows it. Federal limits apply to public water systems; a private well is the owner's responsibility to test (EPA).
% of sampled wells above the EPA limit (latest result per well; counties with 10+ wells). Source: USGS/EPA Water Quality Portal, 2026-10-19 · privatewelldata.com
Nitrate by county in Massachusetts
| County | Above 10 mg/L (as nitrogen) | Median | 90th pct. | Years |
|---|---|---|---|---|
| Nantucket County | 7% of 14 | 0.295 mg/L as N | 2.3 | 1976–1976 |
| Middlesex County | 6% of 158 | 0.81 mg/L as N | 6.24 | 1944–2023 |
| Barnstable County | 5% of 1,705 | 0.53 mg/L as N | 4.5 | 1948–2023 |
| Hampden County | 4% of 69 | 0.43 mg/L as N | 3.5 | 1954–2017 |
| Bristol County | 4% of 25 | 0.171 mg/L as N | 6.1 | 1955–2019 |
| Franklin County | 4% of 53 | 0.61 mg/L as N | 3.8 | 1953–1995 |
| Essex County | 3% of 70 | 0.283 mg/L as N | 5.2 | 1957–2019 |
| Plymouth County | 2% of 131 | 0.407 mg/L as N | 3.637 | 1952–2019 |
| Worcester County | 1% of 126 | 0.24 mg/L as N | 2.6 | 1952–2019 |
| Berkshire County | 0% of 108 | 0.203 mg/L as N | 1.401 | 1953–2017 |
| Norfolk County | 0% of 73 | 1.04 mg/L as N | 3.7 | 1959–2019 |
| Hampshire County | 0% of 24 | 0.545 mg/L as N | 1.7 | 1958–2017 |
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Download this table (CSV) · public-domain source data: Water Quality Portal (USGS, EPA, NWQMC). How we calculate these numbers.
How Massachusetts compares
Share of sampled wells above the EPA nitrate limit in each state we cover (states with 100+ wells).
| # | State | Above 10 mg/L (as nitrogen) |
|---|---|---|
| 1 | California | 10% of 16,344 |
| 2 | Pennsylvania | 8% of 6,478 |
| 3 | Minnesota | 6% of 7,259 |
| 4 | North Carolina | 5% of 1,964 |
| 5 | New York | 5% of 6,236 |
| 6 | Massachusetts | 4% of 2,556 |
| 7 | New Jersey | 4% of 3,915 |
| 8 | Wisconsin | 4% of 3,666 |
| 9 | Virginia | 3% of 1,394 |
| 10 | Maine | 2% of 726 |
| 11 | Michigan | 2% of 1,970 |
| 12 | Ohio | 1% of 1,239 |
| 13 | New Hampshire | 0% of 1,685 |
Where to test: official lab list for Massachusetts
About this data
- Each well counts once, using its latest nitrate result in the Water Quality Portal (siteType = Well), downloaded 2026-10-19.
- Results reported as "not detected" count as below the limit. Results far outside the plausible range are withheld for review, not shown.
- Sampled wells include monitoring and research wells, not only household wells, and are not a random sample, so the share is a guide to local risk, not a rate for all homes.
- The limit is the EPA maximum contaminant level for public water systems (EPA).
Questions
Is nitrate common in Massachusetts well water?
In our data, 106 of 2,556 sampled wells in Massachusetts (4%) had a latest nitrate result above the EPA limit of 10 mg/L (as nitrogen), across 12 counties. That ranks Massachusetts 6 of 13 states we cover for this share.
Which Massachusetts counties have the most wells above the nitrate limit?
Among counties with at least 10 sampled wells: Nantucket County (7%, 1 of 14 wells); Middlesex County (6%, 9 of 158 wells); Barnstable County (5%, 84 of 1705 wells).
Does this tell me whether my well is safe?
No. These are past results from wells sampled by USGS, EPA and state programs, including monitoring wells, and levels differ from well to well. The only way to know your water is to test your own well at a certified lab.
How do I test my well for nitrate in Massachusetts?
Order a nitrate test from a lab on Massachusetts's official certified-lab list (linked on this page) and ask for its bottles and sampling instructions. Our test helper suggests what else to test for at the same time.
What should I do if my nitrate result is above 10 mg/L (as nitrogen)?
Retest to confirm, use another water source for drinking and cooking while you sort it out, and look at certified treatment options. Our guide walks through each step with sources.