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Public water system record

Mercer PWS

Serves Mercer, Mercer County, MO · 318 people served

Federal records show 10 health-based violations and 5 monitoring/reporting issues for Mercer PWS in the last ten years. The most serious issue in this window was a Total Trihalomethanes (TTHMs) violation that EPA lists as archived, not resolved.

  • MO2010515
  • MERCER
  • MO
  • 318 served

System profile

Source water Purchased groundwater
ZIP 64661
EPA system ID MO2010515

Verify this system on EPA ECHO →

Health-based violations, last 10 years
10
Resolved
7
Unresolved
0
Archived by EPA
3
Any acute record
No
Monitoring issues, last 10 years
5

Key facts

  • Mercer PWS buys its water from Princeton PWS.
  • Highest measured level in the last 10 years: Total Trihalomethanes (TTHMs), 97 µg/L, federal limit 80 µg/L (1.2 times the limit), 2024.
  • Record on file since 1992, with 5 health-based violations before October 19, 2016.
  • Lead pipe inventory: 0 lead and 33 unknown out of 186 service lines.

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Health-based violations

Since October 2016

Violation data reflects EPA records through March 2026. For the most current status, visit the EPA ECHO database.

Contaminant Rule family Start date Status Acute
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 84 µg/L, federal limit 80 µg/L (1.1 times the limit)
 220 Oct 1, 2025 Archived
Violation period ended. EPA no longer counts it toward current compliance, but no fix was formally recorded.
 No
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 81.05 µg/L, federal limit 80 µg/L (at or just above the limit)
 220 Jul 1, 2025 Archived
Violation period ended. EPA no longer counts it toward current compliance, but no fix was formally recorded.
 No
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 85 µg/L, federal limit 80 µg/L (1.1 times the limit)
 220 Apr 1, 2025 Archived
Violation period ended. EPA no longer counts it toward current compliance, but no fix was formally recorded.
 No
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 88 µg/L, federal limit 80 µg/L (1.1 times the limit)
 220 Oct 1, 2024 Resolved No
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 97 µg/L, federal limit 80 µg/L (1.2 times the limit)
 220 Jul 1, 2024 Resolved No
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 89.1 µg/L, federal limit 80 µg/L (1.1 times the limit)
 220 Apr 1, 2024 Resolved No
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 85 µg/L, federal limit 80 µg/L (1.1 times the limit)
 220 Oct 1, 2020 Resolved No
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 85 µg/L, federal limit 80 µg/L (1.1 times the limit)
 220 Jul 1, 2020 Resolved No
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 83 µg/L, federal limit 80 µg/L (at or just above the limit)
 220 Apr 1, 2020 Resolved No
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 83 µg/L, federal limit 80 µg/L (at or just above the limit)
 220 Jul 1, 2019 Resolved No

Monitoring and reporting issues

Since October 2016

Missed tests or reports, not contaminants found above a limit.

Issue Start date Status
Haloacetic Acids (HAA5)
Monitoring and reporting
 Jul 1, 2023 Resolved
Total Trihalomethanes (TTHMs)
Monitoring and reporting
 Jul 1, 2023 Resolved
Public Notice
OTHER
 Apr 8, 2021 Resolved
Public Notice
OTHER
 Feb 1, 2021 Resolved
Revised Total Coliform Rule
Monitoring violation
 Oct 1, 2020 Resolved

Full record since 1992

EPA's records for Mercer PWS go back to 1992. Before October 19, 2016 they list 5 health-based violations (4 resolved, 1 archived by EPA without a recorded fix) and 15 monitoring or reporting violations.

Violations that began in Health-based Monitoring and reporting
1990s 4 9
2000s 0 4
2010 to October 18, 2016 1 2
October 19, 2016 to 2019 1 0
2020s 9 5

Most recent health-based violation before October 19, 2016: Total Trihalomethanes (TTHMs), began April 2016, Resolved.

Show all 5 health-based violations before October 19, 2016
Contaminant Start date Status
Total Trihalomethanes (TTHMs)
Contaminant limit exceeded
Measured 82 µg/L, federal limit 80 µg/L (at or just above the limit)
 Apr 1, 2016 Resolved
Total Coliform
Contaminant limit exceeded
 May 1, 1998 Archived
Surface Water Treatment Rule
Treatment technique failure
 Dec 1, 1993 Resolved
Surface Water Treatment Rule
Treatment technique failure
 Aug 1, 1993 Resolved
Surface Water Treatment Rule
Treatment technique failure
 Jul 1, 1993 Resolved

What the violations mean

Total Trihalomethanes (TTHMs)

10 incidents

Disinfection byproduct levels exceeded the federal limit

Long-term TTHM exposure may increase bladder cancer risk

Where the water comes from

Mercer PWS buys its water from Princeton PWS. It lists no wells or intakes of its own. It also has an emergency connection to Mercer County PWSD 1.

Buys water from

Emergency or part-time connections to

Annual water quality report

Mercer PWS must give its customers an annual water quality report (Consumer Confidence Report) by July 1, with the levels its tests found in the previous year.

Systems serving 500 or fewer people may meet the rule by telling customers the report is available on request, so you may need to ask Mercer PWS for a copy.

Find a posted report with EPA's Consumer Confidence Report search

Testing your own water

To test the water at your tap, or a private well this record does not cover, use a laboratory certified for drinking water by Missouri.

Certified drinking water labs by state EPA guidance for private wells