Washington County Water Quality: 4 Cities Ranked by the Records
Washington County, Minnesota: 4 city reports built from EPA and utility records. A county has many suppliers; each city shows the system that serves it.
Highest result for each contaminant
One row per contaminant: the highest result any system in the county reported, against its limit. Open a row for the systems behind it.
Perfluorooctanoic acid (PFOA)Detected in 2 systems of 4 tested4.0 ng/L federal MCL (2024) · US EPAHighest12 ng/L
- Lake Elmo12 ng/LSample date: 2023-02-07 to 2023-08-09
- Stillwater5.2 ng/LSample date: 2024-12-10 to 2025-06-02
- Cottage GroveNot detected · below 4.0 ng/L lab reporting limitSample date: 2024-10-09 to 2025-04-23
- HugoNot detected · below 4.0 ng/L lab reporting limitSample date: 2024-01-31 to 2024-07-24
Perfluorooctanesulfonic acid (PFOS)Detected in 1 system of 4 tested4.0 ng/L federal MCL (2024) · US EPAHighest8.1 ng/L
- Stillwater8.1 ng/LSample date: 2024-12-10 to 2025-06-02
- Cottage GroveNot detected · below 4.0 ng/L lab reporting limitSample date: 2024-10-09 to 2025-04-23
- HugoNot detected · below 4.0 ng/L lab reporting limitSample date: 2024-01-31 to 2024-07-24
- Lake ElmoNot detected · below 4.0 ng/L lab reporting limitSample date: 2023-02-07 to 2023-08-09
LithiumDetected in 1 system of 4 tested10 µg/L EPA health reference level (screening, not a legal limit) · US EPAHighest10.9 µg/L
- Stillwater10.9 µg/LSample date: 2024-12-10 to 2025-06-02
- Cottage GroveNot detected · below 9.0 µg/L lab reporting limitSample date: 2024-10-09 to 2025-04-23
- HugoNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-10-25 to 2024-04-30
- Lake ElmoNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-02-07 to 2023-08-09
Perfluorohexanesulfonic acid (PFHxS)Detected in 1 system of 4 tested10 ng/L federal MCL (2024) · US EPAHighest7.2 ng/L
- Stillwater7.2 ng/LSample date: 2024-12-10 to 2025-06-02
- Cottage GroveNot detected · below 3.0 ng/L lab reporting limitSample date: 2024-10-09 to 2025-04-23
- HugoNot detected · below 3.0 ng/L lab reporting limitSample date: 2024-01-31 to 2024-07-24
- Lake ElmoNot detected · below 3.0 ng/L lab reporting limitSample date: 2023-02-07 to 2023-08-09
Lead (90th percentile)Detected in 2 systems of 4 tested15 µg/L federal action level · US EPAHighest3 µg/L
- Cottage Grove3 µg/LMonitoring period: 2026–2026 (still open)
- Stillwater2 µg/LMonitoring period: 2023–2025
- HugoNot detectedMonitoring period: 2024–2026 (still open)
- Lake ElmoNot detectedMonitoring period: 2021–2023
Perfluorobutanoic acid (PFBA)Detected in 4 systemsNo federal or state limit; shown for transparencyHighest220 ng/L
- Cottage Grove220 ng/LSample date: 2024-10-09 to 2025-04-23
- Lake Elmo140 ng/LSample date: 2023-02-07 to 2023-08-09
- Stillwater118 ng/LSample date: 2024-12-10 to 2025-06-02
- Hugo19.8 ng/LSample date: 2024-01-31 to 2024-07-24
Perfluoropentanoic acid (PFPeA)Detected in 3 systems of 4 testedNo federal or state limit; shown for transparencyHighest6.4 ng/L
- Cottage Grove6.4 ng/LSample date: 2024-10-09 to 2025-04-23
- Stillwater4.5 ng/LSample date: 2024-12-10 to 2025-06-02
- Lake Elmo3.2 ng/LSample date: 2023-02-07 to 2023-08-09
- HugoNot detected · below 3.0 ng/L lab reporting limitSample date: 2024-01-31 to 2024-07-24
24 PFAS tested, none detected in any systemShow
Tested in these 4 systems: Cottage Grove, Hugo, Lake Elmo, Stillwater
- 11-Chloroeicosafluoro-3-oxaundecane-1-sulfonic acid (11Cl-PF3OUdS)
- 1H, 1H, 2H, 2H-perfluorodecane sulfonic acid (8:2 FTS)
- 1H, 1H, 2H, 2H-perfluorohexane sulfonic acid (4:2 FTS)
- 1H, 1H, 2H, 2H-perfluorooctane sulfonic acid (6:2 FTS)
- 4,8-Dioxa-3H-perfluorononanoic acid (ADONA)
- 9-Chlorohexadecafluoro-3-oxanone-1-sulfonic acid (9Cl-PF3ONS)
- Hexafluoropropylene oxide dimer acid (HFPO-DA) (GenX chemicals)
- N-ethyl perfluorooctanesulfonamidoacetic acid (NEtFOSAA)
- N-methyl perfluorooctanesulfonamidoacetic acid (NMeFOSAA)
- Nonafluoro-3,6-dioxaheptanoic acid (NFDHA)
- Perfluoro (2-ethoxyethane) sulfonic acid (PFEESA)
- Perfluoro-3-methoxypropanoic acid (PFMPA)
- Perfluoro-4-methoxybutanoic acid (PFMBA)
- Perfluorobutanesulfonic acid (PFBS)
- Perfluorodecanoic acid (PFDA)
- Perfluorododecanoic acid (PFDoA)
- Perfluoroheptanesulfonic acid (PFHpS)
- Perfluoroheptanoic acid (PFHpA)
- Perfluorohexanoic acid (PFHxA)
- Perfluorononanoic acid (PFNA)
- Perfluoropentanesulfonic acid (PFPeS)
- Perfluorotetradecanoic acid (PFTA)
- Perfluorotridecanoic acid (PFTrDA)
- Perfluoroundecanoic acid (PFUnA)
Cities ranked by the records
Ranked by the Purity Score of each city's main water system, highest first. Scores belong to water systems; there is no county score. The score is computed only from contaminants measured in the published EPA record, so this ranks the record, not which city's water is safest. How the score works.
0of 4 cities above the 15 µg/L action level
Based on each system's 90th-percentile result. Lead from household plumbing isn't in this record.
Lead in MinnesotaLargest water systems
- Cottage GroveCottage Grove · MN182000442,760 served
- StillwaterStillwater · MN182002419,462 served
- HugoHugo · MN182000712,047 served
- Lake ElmoLake Elmo · MN182000910,978 served
Frequently asked
How does Washington County tap water compare across cities?
PurityMap ranks 4 cities in Washington County by the Purity Score of each city's main water system, computed only from contaminants measured in the published EPA record. Scores belong to water systems, not to cities. The highest published score is Hugo's main water system: Hugo · PWSID MN1820007 · Purity Score 100 (Excellent) · Confidence: moderate · Assessed at the water-system level. The ranking compares the records, not which city's water is safest, and your own tap can differ with household plumbing.
How many Washington County cities had a PFAS sample above a 2024 EPA limit?
2 of 4 Washington County city reports had a PFAS sample above a 2024 EPA limit in EPA's UCMR 5 testing, including Lake Elmo (PFOA 12 ng/L), Stillwater (PFOS 8.1 ng/L). That limit is judged on a yearly average, and water systems have until 2029 to meet it, so a single sample is not a violation. PFAS were detected at any level in 4.
Is there lead in Washington County tap water?
Utilities report lead as a 90th-percentile result from home taps. 2 of 4 Washington County cities reported a value above zero, and none was above the 15 µg/L federal action level. Lead usually comes from a building's own pipes and fixtures, so only a test at your tap tells you what you drink.
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