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Stonebridge Mutual Water Co

What EPA’s and California’s records show in this utility’s water: nitrate, arsenic and other regulated chemicals; lead and copper; and violations since 2016, with the certification that handles each result.

Serves
38 people
Connections
15
Water source
Groundwater
Based in
Morgan Hill, CA
County
Santa Clara
Owner
Private
Hardness
Very hard

The short answer

1 result is above the health goal. The worst: Lead, above the health goal. No health-based violations on file since 2016.

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 2026.

Nitrate, chromium (total), arsenic and fluoride: California’s own results, samples taken from Dec. 22, 2025 to Dec. 22, 2025.

Above the health goal1

Lead

Comes from pipes, often your own

Above the health goal

0.6ppb

90th percentile, 2026

In the latest period, 9 in 10 homes sampled were at or below 0.6 ppb, below EPA’s action level of 15 ppb. The action level drops to 10 ppb on Nov. 1, 2027. EPA’s health goal for lead is zero.

What handles it

Below EPA’s limits2

Nitrate

Comes from the source

Below EPA’s limits

0.9ppm

One sample

2025, one sample: 0.9 ppm

The highest sample, in 2025, was 0.9 ppm, below EPA’s legal limit of 10 ppm. That is the only year on file, and its one sample was 0.9 ppm.

What handles it

  • NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
  • NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”

Chromium (total)

Comes from the source

Below EPA’s limits

2.2ppb

Highest yearly average, 2025

Averaged by year, the highest was 2.2 ppb, in 2025, below EPA’s legal limit of 100 ppb. That is the only year on file.

What handles it

2 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Arsenic
  • Fluoride

What handles it

A certification covers specific claims, not a whole standard. Look for these claims on the certifier’s listing, not the box. Wording varies a little: NSF writes “Lead Reduction,” WQA just “Lead.”

At the tap, or for the whole house?

Lead and copper usually come from pipes and fixtures inside or near your home. A whole-house system sits where water enters, so it cannot catch what your own plumbing adds after it. For those, the filter that counts is the one at the tap. How whole-house systems compare.

Filters with those claims on a certifier’s listing

Disclosure: TapBuff earns a commission if you buy through some links on this page. It does not change which standard or filter we name. As an Amazon Associate, TapBuff earns from qualifying purchases. How TapBuff makes money

Compare five-year costs

The best water filters for lead, ranked

Hardness

Very hard, 290 mg/L (17 grains per gallon), at its one sampling point, in 2025.

Hardness is calcium and magnesium. EPA sets no limit for it: it shows up as scale on fixtures and in water heaters, and as soap that won’t lather. USGS calls water above 60 mg/L moderately hard, above 120 hard and above 180 very hard.

Softeners compared at 17 grains per gallon, salt includedSoftener or salt-free conditioner?California water hardness, utility by utility

Violations since 2016

No health-based violations on file with EPA since 2016.

What this report can’t tell you

  • Everything else. Nitrate, chromium (total), arsenic and fluoride results here are California’s own from 2025 on, with EPA’s national file for 2012 to 2019. Stonebridge Mutual Water Co’s own annual report, which it must send you every year, has the contaminants this page does not show.

  • Your own plumbing. Lead results are the 90th percentile across homes the utility samples. Your home’s service line, solder and fixtures decide yours. A certified lab test is the only way to know.

  • What it means for your health. This page reports what the records show and EPA’s limits and goals; it is not medical advice. If you are worried about a health effect, talk to a doctor or your local health department.

  • Anything after the latest data. SDWIS data is from 2026 Q3; UCMR 5 didn’t sample this utility; California’s results run from Dec. 22, 2025 to Dec. 22, 2025.

Testing your own tap

Stonebridge Mutual Water Co’s results are for the water it sends out. What your own service line, solder and fixtures add shows up only in a test of your tap, by a lab California certifies.

No lab California certifies is within 75 miles of the area Stonebridge Mutual Water Co serves on the state’s list. Some take samples by mail; the state’s page lists them all.

All 145 certified labs for California

Sources

PWSID CA4300787. Rebuilt from EPA data on Oct. 18, 2026.

Also in Santa Clara County

All California utilities

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