Santa Clara County water testing turns up different answers depending on which city you live in and which source feeds your tap. Cities on Hetch Hetchy water test the softest and cleanest for PFAS, cities blending in local groundwater run harder and occasionally show trace PFAS, and South County’s private wells carry the county’s clearest nitrate history.
How Does Water Quality Vary Across Santa Clara County?
The county draws on three sources that behave very differently: San Francisco’s Hetch Hetchy reservoir (delivered by SFPUC), Valley Water’s blend of imported and local surface water, and local groundwater wells that individual cities own and operate. Hetch Hetchy water is naturally soft and has never shown a PFAS detection in any city’s testing reviewed for this page.
Valley Water’s surface water runs moderately hard. Local groundwater, pumped from wells beneath each city, runs the hardest and is where nearly every PFAS detection or notable nitrate reading in the county has turned up. Most Santa Clara County cities blend two or three of these sources, which is why two neighborhoods in the same city can report different hardness on the same water quality report. The city-by-city breakdown below draws entirely from each utility’s own 2024 or 2025 Consumer Confidence Report.
Which Santa Clara County Cities Have Detected PFAS?
Most of the county’s public water systems reported no PFAS detected in their most recent testing, and the exceptions are narrow and already being addressed.
- Palo Alto: “We did not detect PFAS in our water,” per the City’s 2024 Annual Water Quality Report; the city runs on 100% Hetch Hetchy supply.
- Sunnyvale: No PFAS detected in UCMR 5 monitoring conducted April 2024 through January 2025, per the City’s 2024 Water Quality Report.
- Santa Clara: No PFAS compounds detected since the City began monitoring in 2019, per its 2024 Consumer Confidence Report.
- Mountain View: No PFAS detected across four consecutive quarters of monitoring completed in 2023, per the City’s 2024 Consumer Confidence Report.
- San Jose (San Jose Water): PFOS was found above state notification levels in six water supply wells; the utility took those wells out of service and has a PFAS treatment facility under construction at Williams Station, with completion expected late 2026 or early 2027, per San Jose Water’s PFAS page.
- Morgan Hill: PFAS has been detected at low levels in a limited number of the city’s 16 groundwater wells since testing began in 2023. PFOA averaged 1.2 parts per trillion and PFOS averaged 0.8 parts per trillion in 2024, both under the federal 4 ppt limit, and the City’s report states the levels “have not reached response level, hence no treatment is currently needed.”
Santa Clara Valley Water District’s own county-wide review reaches a similar conclusion: EPA-mandated testing in 2013-2015 found no PFAS in county groundwater or surface water, and a 2020 round of voluntary testing across 55 monitoring wells found none above the state’s health-advisory levels. If PFAS in your own water is the question you are trying to answer directly, a KELP PFAS panel tests down to the same parts-per-trillion range these utilities use, and how to test for PFAS in water walks through when a home test makes sense versus a lab panel.
Concerned about contaminants in your water?
Get water testing from KETOS KELP using EPA-certified methodology, results you can trust, backed by real data.
Order a Water Test →Which Cities Have Nitrate to Watch?
Nitrate levels in Santa Clara County follow the region’s agricultural history. The numbers differ between north county cities and south county.
North county cities blending in Valley Water report low nitrate: Sunnyvale averaged 3.0 mg/L as nitrogen in its Valley Water supply, Milpitas averaged 0.9 mg/L, and Palo Alto’s 100% Hetch Hetchy supply averaged non-detect, all well under the federal 10 mg/L limit. South county divides by water source. Morgan Hill’s public water system, drawing entirely on groundwater, averaged 3.7 mg/L in 2024, still under the limit, but a 2025 USGS study of the surrounding Gilroy-Hollister groundwater basin found nitrate above the federal limit in 17% of private domestic wells sampled, mostly traced to agricultural fertilizer rather than septic systems. Because of that gap between a well-run public system and the nearby private wells, South County well owners should test independently instead of assuming their neighbor’s public water report applies to them; see well water testing near me for that South Bay-specific guidance.
Which Cities Have the Hardest Water?
Groundwater is the hardness driver everywhere in the county, and cities that lean on local wells test noticeably harder than cities on 100% imported supply.
- Mountain View’s city wells: 220-339 mg/L, in the “very hard” range, though the wells supply only 2% of the city’s water.
- Sunnyvale’s groundwater wells: averaged 290 mg/L, also very hard, versus 111 mg/L from Valley Water and 57 mg/L from SFPUC in the same city.
- Morgan Hill: averaged 267 mg/L countywide, since the city runs entirely on groundwater.
- San Jose Water’s groundwater service areas: range 183-440 mg/L, the widest range found in the county.
- Cupertino (via San Jose Water’s imported supply): 77-153 mg/L, closer to moderate.
- Palo Alto: averaged 60 mg/L, the softest water in the county, reflecting its 100% Hetch Hetchy supply.
Santa Clara County Water Testing by City
| City | Primary source(s) | PFAS status | Nitrate (mg/L as N) | Hardness (mg/L) |
|---|---|---|---|---|
| Palo Alto | 100% SFPUC (Hetch Hetchy) | Not detected (2024) | Non-detect, range to 0.4 | 60 avg, softest in county |
| Sunnyvale | SFPUC, Valley Water, City wells | Not detected (UCMR 5, 2024-2025) | 3.0 avg (Valley Water) | 57-290 depending on source |
| Santa Clara | 61% City wells, 20% SFPUC, 19% Valley Water | Not detected since 2019 | Not separately published | Moderate to hard, groundwater-blended |
| Mountain View | 89% SFPUC, 9% Valley Water, 2% City wells | Not detected (4 quarters through 2023) | Below MCL | 57-339 depending on source |
| San Jose (San Jose Water) | Groundwater, imported, mountain surface water | 6 wells above notification level, offline; treatment facility under construction | Not separately published | 183-440 depending on source |
| Cupertino (San Jose Water) | Imported, Valley Water-sourced | Follows San Jose Water’s system results | Not separately published | 77-153, moderate |
| Milpitas | SFPUC, Valley Water, emergency well | Monitoring ongoing (UCMR 5 through 2025) | 0.9 avg (Valley Water) | 57-110.5 |
| Morgan Hill | 100% groundwater, 16 wells | Detected at low levels in a limited number of wells, under 4 ppt MCL | 3.7 avg | 267 avg, very hard |
| Gilroy area private wells | Private groundwater, Llagas/Gilroy-Hollister basin | Not separately tested for this page | 17% of sampled private wells exceed MCL (USGS, basin-wide) | Not published for private wells |
Is Your Water From a Private Well or a City System?
The city-by-city numbers above describe public water systems, which are tested on a regulatory schedule and published every year. A private well is different: nobody tests it but the owner, on whatever schedule the owner chooses.
If your address falls inside Morgan Hill, Gilroy, San Martin, or the unincorporated hill country, there is a real chance you are on a private well rather than one of the public systems in the table. The county-wide nitrate context above is a good reason to test your own water instead of assuming a public system’s numbers apply to you. Well water testing near me covers where South Bay well owners send a sample and what a South County well specifically should be tested for.
How to Choose the Right Test for Your Situation
Match your test to your address and your specific worry.
- If you are on a public water system and want to confirm what your city reported, or check a fixture-specific concern like plumbing-sourced lead, a general metals-and-chemistry panel is the right starting point.
- If you live in a city with a documented PFAS detection, such as San Jose or Morgan Hill, or near a former industrial site or airport anywhere in the county, add a PFAS panel to the same sample.
- If you are on a private well anywhere in the county, start with the nitrate, TDS, and pH baseline every well needs, and weight nitrate testing more heavily if you are in or near South County.
- If you want metals, minerals, and PFAS answered from a single sample rather than ordering twice, a combined panel covers all three at once.
KETOS Environmental Lab Services
Name: KETOS Environmental Lab Services (KELP)
Address: 520 Mercury Dr, Sunnyvale, CA 94085
Phone: (408) 357-4745
Category: Water testing service
Hours: See current hours on the Google Business Profile
Map: Get directions to 520 Mercury Dr, Sunnyvale, CA 94085
Ready to see your own numbers instead of your city’s average? Order a KELP home water test and get metals, minerals, and water chemistry results in 5 to 7 business days. This page does not cover San Jose-specific pricing and turnaround detail; that is covered at water testing in San Jose. See that page for San Jose-specific guidance, and this page for how San Jose compares to the rest of the county.
Frequently Asked Questions
These four questions come up most often about testing water across the county.
Which Santa Clara County cities have detected PFAS in their water?
San Jose Water found PFOS above state notification levels in six supply wells and took them offline, and Morgan Hill has detected low levels of PFAS in a limited number of its wells, both under the federal 4 parts per trillion limit. Palo Alto, Sunnyvale, Santa Clara, and Mountain View all reported no PFAS detected in their most recent testing.
Does Santa Clara County have a nitrate problem?
Not county-wide. Every public water system reviewed here reports nitrate well under the federal 10 mg/L limit. The exception is private wells in South County, where a 2025 USGS study found nitrate above the limit in 17% of domestic wells sampled in the Gilroy-Hollister groundwater basin.
Which city in Santa Clara County has the hardest water?
Cities and neighborhoods on local groundwater test hardest. Sunnyvale’s groundwater wells average 290 mg/L, Mountain View’s city wells run 220 to 339 mg/L, and Morgan Hill’s entirely groundwater-fed system averages 267 mg/L, all in the “very hard” range. Palo Alto, on 100% Hetch Hetchy water, is the softest at an average of 60 mg/L.
How is this different from KETOS’s San Jose water testing page?
That page covers San Jose-specific KELP pricing, turnaround, and a general PFAS overview. This page covers the county as a whole: which cities’ utilities have found PFAS, where nitrate shows up, and how hardness varies by source, using each city’s own published numbers.
Sources: City of Sunnyvale, City of Santa Clara, City of Palo Alto, City of Mountain View, and City of Milpitas 2024 Consumer Confidence Reports, and City of Morgan Hill July 2024 Consumer Confidence Report, all fetched 2026-09-17 via ear.waterboards.ca.gov and each city’s own website. San Jose Water, water-faqs and PFAS pages (sjwater.com), fetched 2026-09-17. Santa Clara Valley Water District, “What are PFAS, PFOA, and PFOS?” (valleywater.org), fetched 2026-09-17. USGS Scientific Investigations Report 2025-5097, Gilroy-Hollister groundwater basin domestic-well study, published December 1, 2025 (pubs.usgs.gov). California State Water Resources Control Board, PFAS Drinking Water (waterboards.ca.gov), fetched 2026-09-17. EPA National Primary Drinking Water Regulation for PFAS, announced April 10, 2024 (epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas). Full citation list with exact sentence support in substantiation/2026-09-17-art31/sources.md.
