Hardness
Moderately hard average62mg/L as CaCO₃
Source average; range 8.1–112
USGS hardness classes
About 3.6 grains per gallon. Confirm current hardness before deciding on softener capacity.
2025View source
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San Mateo County Water Quality Report
Showing utility report
Cal Water — San Mateo System
2025 utility report; each result retains its measurement period
Results for Cal Water — San Mateo System in San Mateo County. Confirm the supplier and system on your bill.
Your water at a glance
See the amount, the comparison and what it means. “Below” refers to the stated benchmark, not zero risk.
Chloramine
Reported level below MRDL2.7mg/L
Distribution average; range 0.96–3.6
MRDL: 4 mg/L
Match the filter to the disinfectant used by this utility.
2025View source
TTHMs
Reported level below benchmark43µg/L (ppb)
Highest annual average; range 16–54
Report MCL: 80 µg/L
A system result does not measure the water at an individual home.
2025View source
HAA5
Reported level below benchmark39µg/L (ppb)
Highest annual average; range 10–50
Report MCL: 60 µg/L
A system result does not measure the water at an individual home.
2025View source
Fluoride
Below report benchmark0.7mg/L
Source average; range 0.5–0.8
California MCL: 2 mg/L
Standard filtration and softening do not establish fluoride reduction.
2025View source
Lead
90th percentile below action levelNDµg/L (ppb)
90th percentile; 50 sampled sites
Report action level: 15 µg/L
One sampled site exceeded 15 µg/L. A system-wide nondetect percentile does not describe every tap.
2025View source
Your provider needs its own report.
Continue with your home details for general filtration guidance. We will not use another utility’s numbers as your result.
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Explore well-water systems →Water hardness by provider
The figures below are provider-specific. They are not a countywide average.
| Utility | Hardness | Hardness source |
|---|---|---|
| 62 mg/L · Moderately hard average | 2025 |
View Full Water ReportOpen the measured results, dates, comparisons and original utility report.
The numbers behind your report
Selected results with the original sampling dates and measurement basis. Open the utility report for every parameter, notice and footnote.
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| What was measured | Reported amount | Sample year / source date | How to read it |
|---|---|---|---|
| Hardness | 62 mg/L as CaCO₃Source average; range 8.1–112 | 2025View source ↗ | Moderately hard averageAbout 3.6 grains per gallon. Confirm current hardness before deciding on softener capacity. |
| Chloramine | 2.7 mg/LDistribution average; range 0.96–3.6 | 2025View source ↗ | Reported level below MRDLMatch the filter to the disinfectant used by this utility. |
| TTHMs | 43 µg/L (ppb)Highest annual average; range 16–54 | 2025View source ↗ | Reported level below benchmarkA system result does not measure the water at an individual home. |
| HAA5 | 39 µg/L (ppb)Highest annual average; range 10–50 | 2025View source ↗ | Reported level below benchmarkA system result does not measure the water at an individual home. |
| Fluoride | 0.7 mg/LSource average; range 0.5–0.8 | 2025View source ↗ | Below report benchmarkStandard filtration and softening do not establish fluoride reduction. |
| Lead | ND µg/L (ppb)90th percentile; 50 sampled sites | 2025View source ↗ | 90th percentile below action levelOne sampled site exceeded 15 µg/L. A system-wide nondetect percentile does not describe every tap. |
| Nitrate as nitrogen | ND mg/LSource average; range ND–0.4 | 2025View source ↗ | Reported average below benchmarkNitrate requires treatment selected for that specific contaminant. |
In drinking water, ppm ≈ mg/L, ppb ≈ µg/L and ppt ≈ ng/L. Calculated hardness in grains per US gallon (gpg) = mg/L as CaCO₃ ÷ 17.118, rounded to one decimal. ND means below the reporting limit, not zero.
MCL is an enforceable contaminant limit; MRDL is a disinfectant limit. A PHG is a health goal, not the legal limit. Lead/copper action levels use system sampling percentiles, not a safe-tap threshold. TTHM/HAA5 comparisons use locational running annual averages.
PFAS results are compound-specific. Source monitoring, entry-point samples and tap tests are different. Notification and response levels in a utility report are not maximum contaminant levels; do not infer a compliance violation from a single value. EPA PFAS benchmarks and implementation ↗
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Source water. Water purchased from the San Francisco Public Utilities Commission and distributed by Cal Water’s San Mateo System.
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More about your local water
What this means for your home
The reported SFPUC source hardness averages 62 mg/L, with a range of 8.1–112 mg/L.
These are the Cal Water San Mateo System results. Other peninsula cities and water systems can have different distribution measurements even when they purchase water from the same wholesaler.
A useful local question
Does sharing an SFPUC source make every peninsula report identical?
No. Purchased-water characteristics may overlap, but disinfectant residuals, byproducts, and household tap samples can differ by distribution system. Use the report for the retailer on your bill.
Sources and methodology
We keep each utility’s results separate, show the reported sample year, and distinguish averages, maxima and tap-sampling percentiles. Hardness classifications use USGS ranges. Missing data stays unknown.
Different name on your water bill?
These local providers publish separate reports. Follow the matching utility link; the measurements above do not describe these systems.
- Cal Water — San Mateo System ↗2025 utility report; each result retains its measurement period
- USGS hardness classification
- EPA PFAS benchmarks and implementation
Sources checked November 15, 2026
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