Cupertino Tap Water Quality Report
Cupertino's water has 1 contaminant above EPA MCLGs. Consider using a certified water filter for additional protection.
No single water system serves most of Cupertino (58,710 residents, Census 2024 estimate). Its large systems are CITY OF CUPERTINO (EPA counts 16,530 people served, about 28% of Cupertino's population); SAN JOSE WATER (EPA counts 1,007,514 people served, more than Cupertino's population); CWSC LOS ALTOS SUBURBAN (EPA counts 70,175 people served, more than Cupertino's population). EPA's counts may include people served outside Cupertino, so each share is at most that. Check which one bills you: each system's figures are shown separately below.
- CITY OF CUPERTINO: 90 contaminants tested, 1 above EPA MCLGs; health-based violations since 2020: 0
- SAN JOSE WATER: 217 contaminants tested, 2 above EPA MCLGs; health-based violations since 2020: 1
- CWSC LOS ALTOS SUBURBAN: 220 contaminants tested, 3 above EPA MCLGs; health-based violations since 2020: 0
Other systems listed for Cupertino with results above guidelines: SAN JOSE WATER (2 above guidelines), SANTA CLARA VALLEY WATER DISTRICT (2 above guidelines), CWSC LOS ALTOS SUBURBAN (3 above guidelines)
Water systems
3 large systems
Residents (Census 2024)
58,710
Health-based violations since 2020
0
CITY OF CUPERTINO. EPA SDWA violation data as of Q2 2026 (downloaded 2026-07-09).
Latest sample on file
Feb 2025 · CITY OF CUPERTINO
Utilities publish newer results in their annual water quality report (Consumer Confidence Report).
Is Cupertino Tap Water Safe to Drink?
We recommend using a certified water filter for additional protection, especially for vulnerable populations like children, pregnant women, and those with compromised immune systems. Cupertino's water has 1 contaminant above EPA health-based guidelines (MCLGs), while it meets federal legal limits.
CITY OF CUPERTINO, Cupertino's water system, serves 16,530 people. 3 other systems are listed for Cupertino. Each system's results are listed under its own name, never added to CITY OF CUPERTINO's. Water quality testing is conducted regularly and reported to the EPA. The latest sample on file for CITY OF CUPERTINO is from Feb 2025.
Boil water advisories are issued by water systems and state agencies, and they change from day to day. Boil water advisories in California
Cupertino Water Service Areas
What these numbers actually mean for Cupertino, CA
We read Cupertino, CA’s published record and send you a short report — which findings warrant a decision, which to ignore, and what to do about it. Including when the answer is nothing.
- 1 contaminant above EPA MCLGs and 1 nitrate reading above 10 mg/L whose basis is unconfirmed (above EPA's limit if measured as nitrogen, within it if measured as nitrate)
- 26 results on file
- 23 PFAS compounds on record
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Recommended Water Filters for Cupertino
Based on Cupertino's water quality data, these NSF-certified filters are recommended to remove contaminants above EPA MCLGs.
AquaTru
Classic
NSF Certified:
Flow Rate
0.04 gpm
Daily Production
600 gpd
Highlights:
- Best overall contaminant reduction score
- Most performance certifications
- Lifetime warranty
- NSF-42, NSF-53, NSF-58, NSF-401 certified
Removes 23 contaminants:
+18 more
Molybdenum, Barium, Chlorine, Arsenic, 83+ contaminants, Calcium, Chloride, Copper, Magnesium, Nitrate, Phosphorus, Sodium, Sulfate, Total Dissolved Solids, Zinc, Total THMs, Chloroform, Nitrate (as N)
AquaTru
Carafe
NSF Certified:
Flow Rate
0.3 gpm
Daily Production
4 gpd
Highlights:
- Verified PFAS reduction
- Glass collection vessel
- Plug-and-play installation
- NSF-53, NSF-42, NSF-58, NSF-401, NSF-372 certified
Removes 17 contaminants:
+12 more
Arsenic, 83+ contaminants, Copper, Total THMs, Chloroform, Chloride, Sulfate, Nitrate (as N), Molybdenum, Barium, Strontium, Uranium
Waterdrop
G3 P600
NSF Certified:
Flow Rate
600 gpm
Daily Production
600 gpd
Highlights:
- Space-saving design
- Good contaminant reduction
- NSF-58 certified
Removes 4 contaminants:
iSpring Water Systems LLC
RCC7
NSF Certified:
Daily Production
21.04 gpd
Highlights:
- NSF-58 certified reverse osmosis system
- 21.04 GPD production capacity
- Reduces total dissolved solids (TDS) for purer water
Removes 1 contaminants:
Test Your Water Quality
Professional laboratory testing provides accurate, detailed analysis of your drinking water.
SimpleLab
Advanced Home Water Test
$269
Comprehensive water analysis testing over 200 contaminants including bacteria, heavy metals, and chemical compounds.
Tap Score
Advanced Microplastics Test
$829
Cutting-edge testing for microplastics particles in drinking water using advanced laboratory techniques.
Tap Score
Haloacetic Acids (HAA9) Test
$275
Tests for disinfection byproducts formed when chlorine reacts with organic matter in water treatment.
What Cupertino's water readings can explain
Utility-reported data for Cupertino includes a chlorine-based disinfectant — the readings behind these common tap water questions. We publish a city-level hardness figure for Cupertino, resolved from its water systems where they report one and estimated from county sampling where they do not. Each page starts with the hot-tap and cold-tap check, then shows what your own water system reported.
On a private well near Cupertino? Public-water results do not apply to private wells. See Santa Clara County well water testing and USGS risk data — modeled arsenic, nitrate, and the tests to run.
Water softener cost and installation in Cupertino
Cupertino's tap water has an estimated 12.3 grains per gallon (210.0 mg/L, county sampling in Santa Clara County) — very hard on the USGS scale, the range where scale on fixtures and appliances is the usual complaint.
Water softener cost for an estimated 12.3 gpg water in Cupertino — equipment and local installation labour for your ZIP code, with the sizing arithmetic shown in full. For the national picture first, read what a water softener costs — equipment, installation labour and ten-year ownership, each separated out. For California as a whole, read water softener cost in California — priced against the plumber wage published for the state.
Frequently Asked Questions About Cupertino Tap Water
Cupertino's water has 1 contaminant above EPA MCLGs. While the water meets federal legal limits, we recommend using a certified water filter for additional protection, especially for vulnerable populations like children, pregnant women, and those with compromised immune systems.
Spotted something off on this page?
Residents keep our data honest.
This form corrects our data; it does not reach CITY OF CUPERTINO. For a problem with your water now (discolored water, no water, low pressure, a leak), contact CITY OF CUPERTINO directly.
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