Great Bay Water System
What EPA’s and CDC’s records show in this utility’s water: nitrate, arsenic and other regulated chemicals, plus violations since 2016, with the certification that handles each result.
- Serves
- 228 people
- Connections
- 91
- Water source
- Groundwater
- Based in
- Newmarket, NH
- County
- Rockingham
- Owner
- Private
The ZIP code it serves
The short answer
Nothing in EPA’s and CDC’s records for this utility is above a health goal. That covers nitrate, arsenic and other regulated chemicals, not everything. No health-based violations on file since 2016.
What was found
Nitrate, total trihalomethanes (TTHM), arsenic, haloacetic acids (HAA5) and uranium: New Hampshire’s yearly averages per water system, as CDC’s Environmental Public Health Tracking Network publishes them, 2020 to 2023, with EPA’s 2012 to 2019 file for earlier years.
Chromium (total) and fluoride: EPA’s compliance monitoring file, samples taken from Jan. 30, 2014 to Jan. 19, 2017. Newer results are in the utility’s annual water quality report.
Below EPA’s limits3
Nitrate
Comes from the source
0.51ppm
Highest yearly average, 2020 to 2023
2023 average: 0.34 ppm
Averaged by year, the highest was 0.51 ppm, in 2021, below EPA’s legal limit of 10 ppm. In 2023, the latest year on file, it averaged 0.34 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 0.57 ppm, in 2016.
What handles it
- NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
- NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”
Chromium (total)
Comes from the source
2.4ppb
Highest yearly average, 2014 to 2017
Averaged by year, the highest was 2.4 ppb, in 2017, below EPA’s legal limit of 100 ppb. That was also the latest year on file.
What handles it
- NSF/ANSI 58 look for “Chromium (Hexavalent) Reduction”
- NSF/ANSI 53 look for “Chromium Reduction”
Total trihalomethanes (TTHM)
Forms or is added in treatment
1.2ppb
Highest yearly average, 2020 to 2023
Averaged by year, the highest was 1.2 ppb, in 2023, below EPA’s legal limit of 80 ppb. That was also the latest year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 1.2 ppb, in 2019.
What handles it
- NSF/ANSI 53 look for “Trihalomethanes (TTHM) Reduction”
- NSF/ANSI 58 look for “Trihalomethanes (TTHM) Reduction”
4 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
- Arsenic
- Fluoride
- Haloacetic acids (HAA5)
- Uranium
Violations since 2016
No health-based violations on file with EPA since 2016.
What this report can’t tell you
Everything else. Nitrate, total trihalomethanes (TTHM), arsenic, haloacetic acids (HAA5) and uranium results here are New Hampshire’s yearly averages as CDC publishes them, from 2020 on, with EPA’s national file for 2012 to 2019. Chromium (total) and fluoride come from EPA’s file alone, which ends in 2019. Great Bay Water System’s own annual report, which it must send you every year, has newer results for those and the contaminants this page does not show.
Your own plumbing. Lead results are the 90th percentile across homes the utility samples. Your home’s service line, solder and fixtures decide yours. A certified lab test is the only way to know.
What it means for your health. This page reports what the records show and EPA’s limits and goals; it is not medical advice. If you are worried about a health effect, talk to a doctor or your local health department.
Anything after the latest data. SDWIS data is from 2026 Q3; UCMR 5 didn’t sample this utility; CDC’s yearly averages for New Hampshire cover 2020 to 2023; EPA’s compliance samples are from Jan. 30, 2014 to Jan. 19, 2017.
Testing your own tap
The 3 labs New Hampshire certifies closest to the area Great Bay Water System serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.
Seacoast Analytical Services LLC
Lee, NH · about 3 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics
Eurofins Portsmouth
Portsmouth, NH · about 7 miles
Certified for bacteria
Eurofins Derry
Derry, NH · about 21 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, organic chemicals, disinfection byproducts, PFAS
Sources
- EPA UCMR 5 occurrence data, file of Oct. 15, 2026
- EPA SDWA bulk download (SDWIS federal data), 2026 Q3
- CDC Environmental Public Health Tracking Network, yearly averages New Hampshire supplied to CDC, 2020 to 2023, read Oct. 8, 2026. TapBuff’s comparisons with EPA’s limits are its own, not CDC’s or New Hampshire’s.
- EPA Six-Year Review 4 compliance monitoring data, 2012 to 2019, file of Feb. 5, 2024
- Certified labs: New Hampshire ELAP, drinking water labs, as listed in TNI LAMS, read Oct. 13, 2026; distances from the Census 2020 ZIP code tabulation area gazetteer
- Limits and goals: each contaminant’s page, with its EPA source.
- How this page is built: methodology.
PWSID NH1732030. Rebuilt from EPA data on Oct. 18, 2026.
What to do next
- Nothing here is above a health goalIn EPA’s and CDC’s records for this utility. They don’t cover everything, which is why the next step matters.Every contaminant TapBuff tracks
- Get the utility’s own reportGreat Bay Water System must send you a water quality report every year. It covers contaminants this page does not show, and has newer results than EPA’s national file for the ones here that come from it.How to read it
- Test your own tap for leadYour service line, solder and fixtures decide the lead at your faucet, not the utility’s average.Lead in your water: what to do
- Decide if you want a filter at allA filter for taste or chlorine is a preference, not a need. The standards say what each kind can do.NSF/ANSI standards, decoded