Water Quality Report · Updated May 12, 2026
CWSC LOS ALTOS SUBURBAN
CWSC LOS ALTOS SUBURBAN delivers tap water graded F (53/100) by TapWaterSafety.org. The utility serves approximately 69,973 residents in SAN JOSE, California using surface water (purchased). The most significant water quality concerns are: PFAS contamination; Haloacetic acids (HAA5) significantly above health guideline; Perfluorohexane sulfonate (PFHXS) significantly above health guideline; Haloacetic acids (HAA9) significantly above health guideline. For questions, the utility can be reached at 408-367-8593.
Is SAN JOSE tap water safe to drink?
CWSC LOS ALTOS SUBURBAN delivers tap water that earns a grade of F (53/100) from TapWaterSafety.org — a poor rating, with significant contamination concerns and/or recent violations.
The utility serves 69,973 residents in SAN JOSE, drawing from surface water (purchased).
Public testing data identifies 17 contaminants in this water above EWG's health-based guidelines, including: Haloacetic acids (HAA5), Perfluorohexane sulfonate (PFHXS), Haloacetic acids (HAA9), Total trihalomethanes (TTHMs), Bromochloroacetic acid, Bromodichloromethane, Dibromochloromethane, Dibromoacetic acid, Chromium (hexavalent), Nitrate, Nitrate and nitrite, Bromate*, Trichloroacetic acid, Perfluorooctanoic acid (PFOA)*, Bromoform, Chloroform, Dichloroacetic acid. 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.
Quick actions for SAN JOSE residents
Top concerns in this water
Based on the most recent EPA and EWG data, these are the most significant water quality issues for CWSC LOS ALTOS SUBURBAN.
PFAS contamination
Severe concernPerfluorooctanoic acid (PFOA)*, Perfluorooctane sulfonate (PFOS) detected. PFAS are persistent chemicals linked to cancer and immune effects with no known safe exposure threshold.
Haloacetic acids (HAA5) significantly above health guideline
Moderate concernHaloacetic acids (HAA5) detected at 36.2 ppb, 362x above the EWG health guideline of 0.1 ppb.
Perfluorohexane sulfonate (PFHXS) significantly above health guideline
Moderate concernPerfluorohexane sulfonate (PFHXS) detected at 0.345 ppt, 345x above the EWG health guideline of 0.001 ppt.
Haloacetic acids (HAA9) significantly above health guideline
Moderate concernHaloacetic acids (HAA9) detected at 18.0 ppb, 300x above the EWG health guideline of 0.06 ppb.
Contact CWSC LOS ALTOS SUBURBAN
Reach the utility directly for service issues, water quality concerns, or to request your Consumer Confidence Report.
General Contact
Treatment Plant
Recommended water filters for SAN JOSE
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.
Carbon block (NSF/ANSI 42 + 53)
$40-$750Activated carbon is highly effective for disinfection byproducts like TTHM and HAA5.
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 53/100 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 |
|---|---|---|---|---|---|---|---|---|
| Haloacetic acids (HAA5) Disinfection byproduct |
36.2 ppb | 0.1 | 60.0 | 60 | — | — | — | 362× over |
| Perfluorohexane sulfonate (PFHXS) PFAS |
0.345 ppt | 0.001 | 10.0 | — | — | — | — | 345× over |
| Haloacetic acids (HAA9) Disinfection byproduct |
18.0 ppb | 0.06 | — | — | — | — | — | 300× over |
| Total trihalomethanes (TTHMs) Disinfection byproduct |
29.5 ppb | 0.15 | 80.0 | 100 | — | — | — | 197× over |
| Bromochloroacetic acid Disinfection byproduct |
3.04 ppb | 0.02 | — | — | — | — | — | 152× over |
| Bromodichloromethane Disinfection byproduct |
8.02 ppb | 0.06 | — | — | — | — | — | 134× over |
| Dibromochloromethane Disinfection byproduct |
11.0 ppb | 0.1 | — | — | — | — | — | 110× over |
| Dibromoacetic acid Disinfection byproduct |
3.11 ppb | 0.03 | — | — | — | — | — | 104× over |
| Chromium (hexavalent) Heavy metal |
0.951 ppb | 0.02 | — | — | — | — | — | 48× over |
| Nitrate Inorganic |
5.43 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 39× over |
| Nitrate and nitrite Inorganic |
4.13 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 30× over |
| Bromate* Disinfection byproduct |
1.68 ppb | 0.1 | 10.0 | 10 | 10 | 0.1 | — | 17× over |
| Trichloroacetic acid Disinfection byproduct |
1.72 ppb | 0.1 | — | — | — | — | — | 17× over |
| Perfluorooctanoic acid (PFOA)* PFAS |
1.38 ppt | 0.09 | 4.0 | 100 | 100 | 0.007 | — | 15× over |
| Bromoform Disinfection byproduct |
5.77 ppb | 0.5 | — | — | — | — | — | 12× over |
| Chloroform Disinfection byproduct |
4.91 ppb | 0.4 | — | — | — | — | — | 12× over |
| Dichloroacetic acid Disinfection byproduct |
2.47 ppb | 0.2 | — | — | — | — | — | 12× over |
| Chlorate Disinfection byproduct |
174.0 ppb | 210.0 | — | — | — | — | — | Below guideline |
| Radium, combined (-226 and -228) Radiological |
0.04 pCi/L | 0.05 | 5.0 | — | — | — | — | Below guideline |
| Perfluorooctane sulfonate (PFOS) PFAS |
0.226 ppt | 0.3 | 4.0 | 100 | 100 | 1 | — | Below guideline |
| Uranium Radiological |
0.25 pCi/L | 0.43 | 20.0 | 30 | 30 | 0.43 | — | Below guideline |
| Perchlorate Disinfection byproduct |
0.312 ppb | 1.0 | — | — | — | — | — | Below guideline |
| Vanadium Other |
4.72 ppb | 21.0 | — | — | — | — | — | Below guideline |
| Barium Heavy metal |
92.1 ppb | 700.0 | 2000.0 | — | 1300 | 2000 | — | Below guideline |
| Selenium Heavy metal |
1.08 ppb | 30.0 | 50.0 | 20 | 40 | 30 | — | Below guideline |
| Di(2-ethylhexyl) phthalate Semi-volatile organic compound |
0.1 ppb | 3.0 | 6.0 | — | — | — | — | Below guideline |
| Molybdenum Other |
0.932 ppb | 40.0 | — | — | — | — | — | Below guideline |
| N-Nitrosodimethylamine (NDMA)* Other |
0.047 ppt | 3.0 | — | — | — | — | — | Below guideline |
| Monobromoacetic acid Disinfection byproduct |
0.145 ppb | 25.0 | — | — | — | — | — | Below guideline |
| Mercury (inorganic) Heavy metal |
0.0059 ppb | 1.2 | 2.0 | 1 | 6 | 1.2 | — | Below guideline |
| Manganese Heavy metal |
0.491 ppb | 100.0 | — | 50 | 80 | — | — | Below guideline |
| Monochloroacetic acid* Disinfection byproduct |
0.0953 ppb | 53.0 | — | — | — | — | — | Below guideline |
| Perfluoropentanoic Acid (PFPeA)* PFAS |
1.54 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Cobalt Other |
0.0429 ppb | 70.0 | — | — | — | — | — | Below guideline |
| Perfluorobutanoic Acid (PFBA)* PFAS |
0.333 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Strontium Radiological |
0.349 ppb | 1500.0 | — | — | — | — | — | Below guideline |
| Perfluoroheptanoic acid (PFHPA)* PFAS |
0.198 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Perfluorohexanoic Acid (PFHxA) PFAS |
0.086 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Perfluorobutane sulfonate (PFBS) PFAS |
0.022 ppt | 2000.0 | — | — | — | — | — | Below guideline |
| Bromide* Other |
72.3 ppb | — | — | — | — | — | — | Below guideline |
| Chlorodifluoromethane Other |
0.353 ppb | — | — | — | — | — | — | Below guideline |
| Chromium (total) Heavy metal |
1.23 ppb | — | 100.0 | — | — | — | — | Below guideline |
| Cyanide Inorganic |
0.361 ppb | — | 200.0 | 50 | 70 | 150 | — | Below guideline |
| Di-n-butyl phthalate Semi-volatile organic compound |
0.013 ppb | — | — | — | — | — | — | Below guideline |
| Dichlorodifluoromethane Other |
0.078 ppb | — | — | — | — | — | — | Below guideline |
| Fluoride Inorganic |
0.104 ppm | — | 4.0 | 1.5 | 1.5 | — | — | Below guideline |
| Lithium* Other |
2.4 ppb | — | — | — | — | — | — | Below guideline |
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.
CWSC LOS ALTOS SUBURBAN service area
This water system serves 1 community in Santa Clara County, California. Click any city for its dedicated tap water quality page.
Find the right filter for SAN JOSE water
Browse filter categories by water-quality concern. Each option below is NSF-certified for the matched contaminant type.