privatewelldata / Counties / Massachusetts
Barnstable County, Massachusetts
Arsenic: 3 of 123 sampled wells (2%) above the EPA limit of 10 µg/L. Nitrate: 84 of 1705 sampled wells (5%) above the EPA limit of 10 mg/L as N. Samples 1948-05-19 to 2023-12-14; updated 2026-10-18. Source: Water Quality Portal (USGS, EPA, NWQMC), siteType=Well.
What wells in this county have measured for arsenic and nitrate. A local picture only: test your own well to know your water.
Arsenic
3 of 123 sampled wells (2%) had a latest result above the EPA limit of 10 µg/L.
- Median (latest per well)
- 0.78 µg/L
- 90th percentile
- 3.7 µg/L
- Highest
- 19 µg/L
- Non-detects
- 37 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
- Samples
- 126, 1976-01-20 to 2016-05-16
- Source
- Water Quality Portal (USGS, EPA, NWQMC), siteType=Well, downloaded 2026-10-18
Nitrate
84 of 1705 sampled wells (5%) had a latest result above the EPA limit of 10 mg/L as N.
- Median (latest per well)
- 0.53 mg/L as N
- 90th percentile
- 4.5 mg/L as N
- Highest
- 74.546 mg/L as N
- Non-detects
- 401 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
- Samples
- 6362, 1948-05-19 to 2023-12-14
- Source
- Water Quality Portal (USGS, EPA, NWQMC), siteType=Well, downloaded 2026-10-18
Includes monitoring, research and private wells reported to the Water Quality Portal. Non-detects count only when the lab's detection limit is at or below the EPA limit. Method: data rules.
What to do next
- Test your own well. County numbers cannot tell you what is in your water. See which tests fit your well.
- Use a lab certified by Massachusetts. Certified labs in Massachusetts.
- Compare your results with the EPA limits (arsenic 10 µg/L, nitrate 10 mg/L as N). If a result is above a limit, contact your county or state health department.
- If a result is high: arsenic guide · nitrate guide · bacteria guide · salesperson checklist.
- Test again every year for bacteria and nitrate. Get a yearly reminder.