Updated
San Jose's tap water depends on which of three sources reaches you
San Jose Water has served the South Bay since 1866. It serves most of the city (some neighborhoods get water from Great Oaks Water or the city-owned San Jose Municipal Water instead). Unlike a city on a single river, its customers get a changing blend of local mountain streams, groundwater wells and imported surface water treated by Valley Water. Hardness and PFAS both depend on that blend.
The three sources compared
| 2025 average | Mountain surface | Groundwater | Valley Water surface |
|---|---|---|---|
| Hardness | 151 ppm (9 gpg) | 288 ppm (16.8 gpg) | 99 ppm (5.8 gpg) |
| Sodium | 21 ppm | 27 ppm | 48 ppm |
| Total dissolved solids | 200 ppm | 397 ppm | 247 ppm |
| Chromium-6 | 0.617 ppb (max) | 4.67 ppb | not detected |
Groundwater hardness ranged from 175 to 451 ppm, so homes fed mainly by wells can see hardness above 25 grains per gallon. That's enough to make a softener worth pricing. Use our sizing calculator, and set it for the high end of your area's range.
Watershed risks
The state's assessment found San Jose Water's own surface supplies most vulnerable to low-density septic systems. Imported Valley Water supplies are exposed to farm and urban runoff, recreation, grazing and development. Local sources also face risks from commercial stables and historic mining. The utility says physical barriers, treatment and monitoring keep those risks from reaching customers. In 2025, Giardia averaged 0.22 cysts/L in untreated mountain water, which is why surface water is filtered and disinfected. Turbidity standards were met 100% of the time.
A PFAS program that started early
San Jose Water started testing for PFAS in 2019. It has since collected more than 16,000 samples from about 97 locations: 88 wells and 9 Santa Cruz Mountains surface sources. The pattern is clear. The mountain water is essentially PFAS-free, and the problem is in some wells:
- PFHxS: several wells averaged above California's 3 ppt notification level. The highest active-well average was 5.97 ppt.
- PFOS: above 4 ppt at only 2 of 76 active wells, both at Williams Station.
- PFOA: not detected above 4 ppt at any well.
The utility is responding in two ways. It voluntarily took 10 wells off line between 2019 and 2024 (8 of them for higher PFOS), and its Williams Station PFAS treatment facility is fully designed, with construction expected in 2026/2027. Until then, a filter certified for PFOA/PFOS is the household option. Our filter selector compares the choices, and the RO output and waste calculator shows what an under-sink RO system really costs in water.
Lead and copper
San Jose Water published a full service line inventory online and calls eliminating lead service lines a key commitment. Tap sampling in 2025:
- Spring: 103 homes, lead 90th percentile 2.1 ppb (max 17), 1 home above the action level.
- Fall: 102 homes, lead 90th percentile 1.6 ppb, 1 home above, with a single reading of 810 ppb.
- Copper: 90th percentiles of 0.58 and 0.56 ppm, with 1 home above 1.3 ppm in each round.
A single result as high as 810 ppb almost always comes from the plumbing at that one address. If your building's plumbing is old, testing is cheap reassurance.
San Jose water questions
Why is my San Jose water harder than my friend's across town?
San Jose Water serves a blend from three source types, and the mix differs by neighborhood. In 2025, groundwater averaged 288 ppm hardness (16.8 gpg, range 10.2–26.4 gpg), Santa Cruz Mountains surface water about 151 ppm (9 gpg), and Valley Water's treated surface water about 99 ppm (5.8 gpg). Call (408) 279-7900 to find out which source usually supplies your street.
Does San Jose Water have PFAS?
Some of its wells do. PFHxS is the compound found most often in groundwater. The highest average at a well actively serving customers was 5.97 ppt, above California's 3 ppt notification level but below the 10 ppt response level. PFOS was above 4 ppt at 2 of 76 active wells, both at Williams Station, where a treatment facility is designed and construction is expected to start in 2026/2027. Ten wells were voluntarily taken off line between 2019 and 2024.
Is mountain surface water better?
For PFAS, yes. San Jose Water's Santa Cruz Mountains sources averaged about 1 ppt or less for the three main PFAS compounds. The utility protects more than 6,000 acres of watershed land there. That water is also softer than the groundwater.
Sources
- San Jose Water, 2025 Consumer Confidence Report
- EPA UCMR 5 data finder
- California DDW PFAS notification and response levels
Reviewed November 1, 2026 against the sources above. Public water system ID CA4310011 (San Jose Water). Figures describe the utility's system, not your home's plumbing; a certified lab test tells you what comes out of your tap. Spot an error? Tell us.