Tap Water Quality Report
Tap water quality in Modesto, California
Tap water in Modesto, California receives a grade of F (49/100) from TapWaterSafety.org. It's served by City of Modesto Water Department. The most significant water quality concerns are: PFAS contamination; Arsenic significantly above health guideline; Chromium-6 detected; Radium-228 detected. Data sources: EPA SDWIS, EPA ECHO, EWG Tap Water Database, and Modesto's published Consumer Confidence Report.
What's in Modesto's tap water
Top water quality concerns identified by the EPA and Environmental Working Group across the utility serving Modesto.
PFAS contamination
Severe concernPFOA, PFOA detected. PFAS are persistent chemicals linked to cancer and immune effects with no known safe exposure threshold.
Arsenic significantly above health guideline
Moderate concernArsenic detected at 3.96 ppb, 990x above the EWG health guideline of 0.004 ppb.
Chromium-6 detected
Moderate concernChromium-6 detected at 0.4 ppb.
Radium-228 detected
Moderate concernRadium-228 detected at 0.39 pCi/L.
Recommended filters for Modesto
Filters matched to the specific contaminants in Modesto's water supply.
Reverse Osmosis or NSF P473 certified carbon
$80-$750Activated carbon and RO are the only technologies proven to remove PFAS at certified levels.
Reverse Osmosis
$249-$750Arsenic is most effectively removed by reverse osmosis. Some specialized adsorptive filters also work.
Reverse Osmosis or water softener
$249-$750RO removes radium effectively; ion-exchange water softeners also reduce radium concentration.
Disclosure: TapWaterSafety earns a commission from purchases made through these links. This does not influence our scoring methodology or filter selection.
All contaminants detected in Modesto's tap water
Every contaminant identified, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal. Why we show multiple standards →
| Contaminant | Detected | EWG US health-based |
EPA US legal |
EU DWD Europe |
WHO global |
CA PHG strictest US |
Tested sample year |
Status |
|---|---|---|---|---|---|---|---|---|
| Arsenic Heavy metal |
3.96 ppb | 0.004 | 10 | 10 | 10 | 0.004 | 2023 | 990× over |
| PFOA Organic |
2.62 ppt | 0.004 | 4 | 100 | 100 | 0.007 | 2023 | 655× over |
| Haloacetic Acids (HAA5) Disinfection byproduct |
6.3 ppb | 0.1 | 60 | 60 | — | — | 2024 | 63× over |
| Radium-228 Radiological |
0.504 pCi/L | 0.019 | 5 | — | 0.1 | 0.019 | 2022 | 27× over |
| Chromium-6 (Hexavalent) Heavy metal |
0.437 ppb | 0.02 | — | — | — | 0.02 | 2023 | 22× over |
| Total Trihalomethanes (TTHMs) Disinfection byproduct |
5.04 ppb | 0.6 | 80 | 100 | — | — | 2023 | 8.4× over |
| Contaminant | Detected (2024) | EWG | EPA | EU DWD | WHO | CA PHG | Status |
|---|---|---|---|---|---|---|---|
| Haloacetic Acids (HAA5) Disinfection byproduct |
6.3 ppb | 0.1 | 60 | 60 | — | — | 63× over |
| Contaminant | Detected (2023) | EWG | EPA | EU DWD | WHO | CA PHG | Status |
|---|---|---|---|---|---|---|---|
| Arsenic Heavy metal |
3.96 ppb | 0.004 | 10 | 10 | 10 | 0.004 | 990× over |
| PFOA Organic |
2.62 ppt | 0.004 | 4 | 100 | 100 | 0.007 | 655× over |
| Chromium-6 (Hexavalent) Heavy metal |
0.437 ppb | 0.02 | — | — | — | 0.02 | 22× over |
| Total Trihalomethanes (TTHMs) Disinfection byproduct |
5.04 ppb | 0.6 | 80 | 100 | — | — | 8.4× over |
| Contaminant | Detected (2022) | EWG | EPA | EU DWD | WHO | CA PHG | Status |
|---|---|---|---|---|---|---|---|
| Radium-228 Radiological |
0.504 pCi/L | 0.019 | 5 | — | 0.1 | 0.019 | 27× over |
All values in the unit of the detected level. Red cells indicate the detected level exceeds that standard. Some contaminants have limits in some jurisdictions but not others (shown as —). The "Tested" column shows the year each contaminant sample was collected.
Sources: US EPA, EU Drinking Water Directive 2020/2184, WHO Guidelines, California OEHHA PHGs, EWG Tap Water Database.
Treatment plant contact info
For service issues, water quality concerns, or to request a Consumer Confidence Report from City of Modesto Water Department.
General Contact
Water Quality Contact
For questions about contaminants or test results.