What's in your tap water, and what it costs
Cupertino has three different water systems. Which one you're on depends on your street, and it changes your water's hardness, your bill, and what's been found in it.
Last checked Oct 20, 2026 · Water quality from the 2025 reports (published June 2026) · Rates effective July 1, 2026
Which system serves you
San Jose Water
State system CA4310011. Roughly south of Highway 280. Bills every two months.
Cal Water, Los Altos Suburban
State system CA4310001.
City of Cupertino water
State system CA4310018, about 4,600 homes. Owned by the city, run by San Jose Water under a lease through 2036.
Enter your address on the main page and we look it up on the State Water Board's official boundary map.
Where it comes from
All three blend water from up to three sources, in a mix that changes by neighborhood and season:
- Local groundwater from wells. Very hard, and the source of most PFAS detections.
- Valley Water treated water: imported state and federal project water plus local reservoirs, treated at Valley Water's plants. Moderately hard.
- Mountain streams (San Jose Water only), from the Santa Cruz Mountains.
Neighbors to the north get mostly Hetch Hetchy water from Yosemite: about 90% in Mountain View and 56% in Sunnyvale. It is much softer.
What's in it (2025 tests)
| Measure | San Jose Water | Cal Water | What it means |
|---|---|---|---|
| Hardness | 99–288 ppm by source (6–17 grains/gal) | 97–305 ppm | Groundwater is very hard. It leaves scale on fixtures and shortens water-heater life. Above about 10 grains/gal, many owners install a softener. |
| Disinfectant | Chloramine and/or chlorine | Chloramine | Safe to drink. It must be removed for fish tanks, and dialysis patients should talk to their clinic. |
| PFAS (PFHxS) | Groundwater avg 3.2 ppt, up to 9.8 | Up to 4.1 ppt, avg not detected | The state notification level is 3 ppt. The report gives the response level as 20 ppt in its tables and 10 in its text. San Jose Water found PFOS above the notification level at 2 of 76 wells and plans treatment in 2026–27. |
| Nitrate | Avg 3.1 ppm (limit 10) | Avg 4.1, max 7.8 ppm | Below the legal limit. It comes from old farming and septic use in the groundwater. |
| Sodium | 21–48 ppm | 33–52 ppm | Low. Matters only on a strict low-sodium diet. |
| Lead | See note | Not detected (0 of 31 homes over) | The legal action level is 15 ppb at the 90th percentile. |
| Violations | None | None |
Its table shows lead at 2.1 and 1.6 ppb (90th percentile), with one home over the action level in each round, while its text says lead was below detection. We won't summarize it until San Jose Water corrects one or the other. If you have an older house or old faucets, a lab lead test costs about $30–50.
The City of Cupertino system is covered by San Jose Water's report, with no separate figures.
What you pay
| San Jose Water | Cal Water | |
|---|---|---|
| Monthly service charge (standard meter) | $79.67 | $47.56 |
| First 6 units | $5.04 | $2.77 |
| Next 6 units | $7.52 | $11.05 |
| Above 12 units | $14.35 | $11.05–16.58 |
| Typical month (9 units) | ~$138 | ~$97 |
1 unit (CCF) = 748 gallons. San Jose Water also adds a temporary $0.30/unit surcharge and a $2.61 monthly assistance-program fee, both included in the typical month. The City of Cupertino system has its own, lower rates; we haven't found the current table yet. Sewer isn't on your water bill: in Cupertino it's on your property tax bill.
Same house, same use, different street: about $490 a year apart.
Ways to pay less
Stay out of the top tier
$14.35 per unit above 12San Jose Water's top tier costs almost three times the first. Summer lawn watering is what usually pushes a house over.
Replace lawn: $2 per square foot back
Up to $3,000Valley Water pays $2/sq ft for converting lawn to water-wise landscaping, up to $3,000 per home. Funded through June 30, 2027. You must apply and get approval before removing the lawn.
How: valleywater.org/saving-water/rebates-surveys/landscape-rebates
Laundry-to-landscape: $200
Send washing-machine water to your garden. Valley Water also rebates drip irrigation and rain barrels, and offers free water-wise house calls.
Low-income discount: 15% off
San Jose Water's Customer Assistance Program takes 15% off the whole bill and uses the same income limits as PG&E CARE, but it's a separate application. Cal Water has its own program.
Facts are checked against the public sources listed on each page. Rates change every year; each page shows when it was last checked. Individual bills are confidential in California, so personal numbers are estimates from public rates. Nothing here is legal, tax or insurance advice.