Water Quality Report · Updated May 12, 2026
City of Modesto Water Department
City of Modesto Water Department delivers tap water graded F (49/100) by TapWaterSafety.org. The utility serves approximately 214,000 residents in Modesto, California using groundwater blended from the Modesto Reservoir/Tuolumne River. The most significant water quality concerns are: PFAS contamination; Arsenic significantly above health guideline; Chromium-6 detected; Radium-228 detected. For questions, the utility can be reached at (213) 335-8768.
Is Modesto tap water safe to drink?
City of Modesto Water Department delivers tap water that earns a grade of F (49/100) from TapWaterSafety.org — a poor rating, with significant contamination concerns and/or recent violations.
The utility serves 214,000 residents in Modesto, drawing from groundwater blended (Modesto Reservoir/Tuolumne River) and disinfecting with chloramine.
Public testing data identifies 18 contaminants in this water above EWG's health-based guidelines, including: Arsenic, Arsenic, Arsenic, PFOA, PFOA, PFOA, Haloacetic Acids (HAA5), Haloacetic Acids (HAA5), Haloacetic Acids (HAA5), Radium-228, Radium-228, Chromium-6 (Hexavalent), Radium-228, Chromium-6 (Hexavalent), Chromium-6 (Hexavalent), Total Trihalomethanes (TTHMs), Total Trihalomethanes (TTHMs), Total Trihalomethanes (TTHMs). For most residents, a properly certified home filter at the kitchen tap is the most cost-effective way to reduce exposure to whatever's in your water. See our filter recommendations below, matched specifically to this utility's contaminant profile.
Top concerns in this water
Based on the most recent EPA and EWG data, these are the most significant water quality issues for City of Modesto Water Department.
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.
Contact City of Modesto Water Department
Reach the utility directly for service issues, water quality concerns, or to request your Consumer Confidence Report.
General Contact
Water Quality Contact
For questions about contaminants, test results, or your Consumer Confidence Report.
Treatment Plant
Recommended water filters for Modesto
Filters matched to the specific contaminants in this 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.
Score breakdown
This utility's overall score of 49/100 breaks down across five weighted components. Read the full methodology →
Contaminants detected — international standards comparison
Every contaminant detected, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal (the strictest US benchmark). 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 |
| Arsenic Heavy metal |
3.7 ppb | 0.004 | 10 | 10 | 10 | 0.004 | 2022 | 925× over |
| Arsenic Heavy metal |
3.3 ppb | 0.004 | 10 | 10 | 10 | 0.004 | 2024 | 825× over |
| PFOA Organic |
2.62 ppt | 0.004 | 4 | 100 | 100 | 0.007 | 2023 | 655× over |
| PFOA Organic |
2.2 ppt | 0.004 | 4 | 100 | 100 | 0.007 | 2024 | 550× over |
| PFOA Organic |
1.94 ppt | 0.004 | 4 | 100 | 100 | 0.007 | 2022 | 485× over |
| Haloacetic Acids (HAA5) Disinfection byproduct |
6.3 ppb | 0.1 | 60 | 60 | — | — | 2024 | 63× over |
| Haloacetic Acids (HAA5) Disinfection byproduct |
5.81 ppb | 0.1 | 60 | 60 | — | — | 2023 | 58× over |
| Haloacetic Acids (HAA5) Disinfection byproduct |
5.01 ppb | 0.1 | 60 | 60 | — | — | 2022 | 50× over |
| Radium-228 Radiological |
0.504 pCi/L | 0.019 | 5 | — | 0.1 | 0.019 | 2022 | 27× over |
| Radium-228 Radiological |
0.416 pCi/L | 0.019 | 5 | — | 0.1 | 0.019 | 2023 | 22× over |
| Chromium-6 (Hexavalent) Heavy metal |
0.437 ppb | 0.02 | — | — | — | 0.02 | 2023 | 22× over |
| Radium-228 Radiological |
0.39 pCi/L | 0.019 | 5 | — | 0.1 | 0.019 | 2024 | 20× over |
| Chromium-6 (Hexavalent) Heavy metal |
0.4 ppb | 0.02 | — | — | — | 0.02 | 2024 | 20× over |
| Chromium-6 (Hexavalent) Heavy metal |
0.282 ppb | 0.02 | — | — | — | 0.02 | 2022 | 14× over |
| Total Trihalomethanes (TTHMs) Disinfection byproduct |
5.04 ppb | 0.6 | 80 | 100 | — | — | 2023 | 8.4× over |
| Total Trihalomethanes (TTHMs) Disinfection byproduct |
5.03 ppb | 0.6 | 80 | 100 | — | — | 2022 | 8.4× over |
| Total Trihalomethanes (TTHMs) Disinfection byproduct |
4.1 ppb | 0.6 | 80 | 100 | — | — | 2024 | 6.8× over |
| Contaminant | Detected (2024) | EWG | EPA | EU DWD | WHO | CA PHG | Status |
|---|---|---|---|---|---|---|---|
| Total Trihalomethanes (TTHMs) Disinfection byproduct |
4.1 ppb | 0.6 | 80 | 100 | — | — | 6.8× over |
| Haloacetic Acids (HAA5) Disinfection byproduct |
6.3 ppb | 0.1 | 60 | 60 | — | — | 63× over |
| Arsenic Heavy metal |
3.3 ppb | 0.004 | 10 | 10 | 10 | 0.004 | 825× over |
| Radium-228 Radiological |
0.39 pCi/L | 0.019 | 5 | — | 0.1 | 0.019 | 20× over |
| Chromium-6 (Hexavalent) Heavy metal |
0.4 ppb | 0.02 | — | — | — | 0.02 | 20× over |
| PFOA Organic |
2.2 ppt | 0.004 | 4 | 100 | 100 | 0.007 | 550× over |
| Contaminant | Detected (2023) | EWG | EPA | EU DWD | WHO | CA PHG | Status |
|---|---|---|---|---|---|---|---|
| Total Trihalomethanes (TTHMs) Disinfection byproduct |
5.04 ppb | 0.6 | 80 | 100 | — | — | 8.4× over |
| Haloacetic Acids (HAA5) Disinfection byproduct |
5.81 ppb | 0.1 | 60 | 60 | — | — | 58× over |
| Arsenic Heavy metal |
3.96 ppb | 0.004 | 10 | 10 | 10 | 0.004 | 990× over |
| Radium-228 Radiological |
0.416 pCi/L | 0.019 | 5 | — | 0.1 | 0.019 | 22× over |
| Chromium-6 (Hexavalent) Heavy metal |
0.437 ppb | 0.02 | — | — | — | 0.02 | 22× over |
| PFOA Organic |
2.62 ppt | 0.004 | 4 | 100 | 100 | 0.007 | 655× over |
| Contaminant | Detected (2022) | EWG | EPA | EU DWD | WHO | CA PHG | Status |
|---|---|---|---|---|---|---|---|
| Total Trihalomethanes (TTHMs) Disinfection byproduct |
5.03 ppb | 0.6 | 80 | 100 | — | — | 8.4× over |
| Haloacetic Acids (HAA5) Disinfection byproduct |
5.01 ppb | 0.1 | 60 | 60 | — | — | 50× over |
| Arsenic Heavy metal |
3.7 ppb | 0.004 | 10 | 10 | 10 | 0.004 | 925× over |
| Radium-228 Radiological |
0.504 pCi/L | 0.019 | 5 | — | 0.1 | 0.019 | 27× over |
| Chromium-6 (Hexavalent) Heavy metal |
0.282 ppb | 0.02 | — | — | — | 0.02 | 14× over |
| PFOA Organic |
1.94 ppt | 0.004 | 4 | 100 | 100 | 0.007 | 485× 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 (4th ed.), California OEHHA PHGs, EWG Tap Water Database, and City of Modesto Water Department's Consumer Confidence Report.
City of Modesto Water Department service area
This water system serves 1 community in Stanislaus County, California. Click any city for its dedicated tap water quality page.
Find the right filter for Modesto water
Browse filter categories by water-quality concern. Each option below is NSF-certified for the matched contaminant type.