Washington County, Maine

Arsenic: 13 of 39 sampled wells (33%) above the EPA limit of 10 µg/L. Nitrate: 0 of 51 sampled wells (0%) above the EPA limit of 10 mg/L as N. Samples 1968-05-28 to 2023-07-11; 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

13 of 39 sampled wells (33%) had a latest result above the EPA limit of 10 µg/L.

Median (latest per well): 1 µg/L
90th percentile: 100 µg/L
Highest: Withheld for review: 2 wells' latest result was above 1000 µg/L, far outside the usual range. They are still counted as above the limit.
Non-detects: 1 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
Samples: 61, 1980-10-21 to 2023-07-11
Source: Water Quality Portal (USGS, EPA, NWQMC), siteType=Well, downloaded 2026-10-18

Nitrate

0 of 51 sampled wells (0%) had a latest result above the EPA limit of 10 mg/L as N.

Median (latest per well): 0.03 mg/L as N
90th percentile: 0.33 mg/L as N
Highest: 0.6 mg/L as N
Non-detects: 8 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
Samples: 80, 1968-05-28 to 2023-07-11
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 Maine. Certified labs in Maine.
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.