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Not health advice. Contact your local water utility for concerns.
Data from EPA Water Quality Reports. For official information, contact your water utility or health department.
Water quality data for 4 cities serving 441,111 residents
San Joaquin County in California has an average water quality score of 78/100 (Grade C) based on analysis of 4 municipal water systems. The county's water systems serve approximately 441,111 residents.
Water quality in San Joaquin County is fair, with some cities showing room for improvement. 1 cities have scores below 70, indicating elevated contaminant levels that residents should be aware of. Tracy has the best water quality at 100/100.
4 cities ranked by water quality score
| Rank | City | Score | Grade | Population |
|---|---|---|---|---|
| 1 | Tracy | 100 | A | 96,609 |
| 2 | Manteca Biggest deduction: PFOA detected at up to 7 ppt in UCMR5 sampling (2025-10-21), at or above EPA's 4 ppt MCL (−10 pts) | 80 | B | 84,928 |
| 3 | Lodi Biggest deduction: PFOA detected at up to 6.2 ppt in UCMR5 sampling (2025-07-28), at or above EPA's 4 ppt MCL (−10 pts) | 74 | C | 68,272 |
| 4 | Stockton Biggest deduction: 2 health-based violations (MCL/treatment-technique) in the last 5 years (−20 pts) | 56 | F | 191,302 |
Real EPA readings across county water systems (lead: latest 90th percentile; PFAS: UCMR5 2023–2026; others: 2012–2019 averages)
| Contaminant | Avg Level | Max Level | EPA Limit | % of Limit | Cities |
|---|---|---|---|---|---|
| PFAS (PFOA/PFOS max, UCMR5) | 13.3 ppt | 28 ppt | 4 ppt | 332.5% | 4 |
| TTHM (2012–2019 avg) | 32.078 ug/L | 41.134 ug/L | 80 ug/L | 40.1% | 4 |
| HAA5 (2012–2019 avg) | 18.125 ug/L | 24.184 ug/L | 60 ug/L | 30.2% | 4 |
| Uranium (2012–2019 avg) | 8.312 ug/L | 16.39 ug/L | 30 ug/L | 27.7% | 2 |
| Nitrate (2012–2019 avg) | 2.283 mg/L | 5.001 mg/L | 10 mg/L | 22.8% | 4 |
| Arsenic (2012–2019 avg) | 1.131 ug/L | 4.153 ug/L | 10 ug/L | 11.3% | 4 |
| Lead (90th percentile) | 0.1 ppb | 0.4 ppb | 15 ppb | 0.7% | 4 |
| Fluoride (2012–2019 avg) | 0 mg/L | 0 mg/L | 4 mg/L | 0% | 3 |
Recent violations across county water systems
Health-based: Treatment technique — Treatment Technique (SWTR and GWR) - Surface Water Treatment Rule
2/29/2016
Water quality in San Joaquin County, California reflects the region's unique combination of water sources, treatment infrastructure, and environmental factors. Our comprehensive analysis examines 4 municipal water systems serving a combined population of over 441,111 residents.
The county shows moderate water quality performance, with scores ranging from 56/100 in Stockton to 100/100 in Tracy. This 44-point spread indicates significant variation in water quality across the county, suggesting different water sources or treatment approaches.
The most prevalent contaminants detected across San Joaquin County water systems include PFAS (PFOA/PFOS max, UCMR5), TTHM (2012–2019 avg), HAA5 (2012–2019 avg). At least one reading averages above 50% of its EPA limit across the county's systems, worth attention from residents and utilities.
Water quality in San Joaquin County is fair but shows room for improvement. Residents in cities scoring below 70 should consider water filtration, particularly for drinking and cooking. Check your specific city's report above for personalized recommendations.
San Joaquin County has an average water quality score of 78/100 (Grade C) based on analysis of 4 municipal water systems serving 441,111 residents.
Tracy has the highest water quality score in San Joaquin County at 100/100. View the detailed report for Tracy.
Given the water quality variation across San Joaquin County, we recommend reviewing your specific city's water quality report. 1 cities have scores below 70, where filtration is particularly recommended.
Click on any city in the rankings table above to view its detailed water quality report, including contaminant levels, EPA compliance history, and filter recommendations.