San Mateo County | Public water system SAFER profile
Data date: September 23, 2026
Page 1 of 3

San Mateo County public water systems

Failing or At-Risk
9systems
3,598people served (0% of total)
Not At-Risk or Not Assessed
25systems
768,147people served (99% of total)
includes Not Assessed systems, which are outside the SAFER assessment

Status classification

Share of listed systems, followed by the count, reported population, and funding in each status.

Failing11%
At-Risk14%
Not At-Risk64%
Failing
At-Risk
Potentially At-Risk
Not At-Risk
Not Assessed
Systems
4
5
2
23
2
Population
3,018
580
1,313
562,018
206,129
Funding since 2017
$0
$0
$0
$0
$0

Key figures

36
public water systems
773,058
reported population
36%
serve 500 people or fewer
$0
reported funding since 2017

System locations

Points show reported system locations. They do not represent service-area boundaries.

Each point represents one system record.

Summary

San Mateo County has 36 public water systems in the SAFER dataset. Of these, 9 (25%) are classified as Failing or At-Risk.

Those systems report serving 3,598 people. The county profile is also shaped by small systems: 13 systems serve 500 people or fewer.

2 systems are Not Assessed. These fall outside the SAFER risk assessment, so they carry no classification either way.

Reported funding since 2017 totals $0 across 0 systems. Technical assistance funding totals $984K.

System counts and reported population

Not Assessed systems make up 6% of listed systems and 27% of reported population. A few large systems account for most of that population, so a small number of systems can shift the population picture entirely. Counts and population are worth reading together.

San Mateo County | Public water system SAFER profile
Data date: September 23, 2026
Page 2 of 3

Risk profile

Risk in San Mateo County is distributed across four dimensions. Accessibility contributes the largest share of the combined weighted risk score at 42%. Across all individual indicators, Total net annual income appears most often, affecting 18 of 34 assessed systems.

Water Quality
24%
of combined weighted risk
State 33% · ▼ 9 pts
Most common flagWater quality trends toward MCL
Accessibility
42%
of combined weighted risk
State 36% · ▲ 6 pts
Most common flagNo intertie
Affordability
12%
of combined weighted risk
State 17% · ▼ 5 pts
Most common flagHousehold socioeconomic burden
TMF Capacity
23%
of combined weighted risk
State 14% · ▲ 8 pts
Most common flagTotal net annual income

Water Quality

Water Quality accounts for 24% of the county’s combined weighted risk score. Water quality trends toward MCL appears in 10 of 34 assessed systems. Past presence on Failing list is next, appearing in 9 of 34 assessed systems.

Each indicator was assessed for 34 systems.

Accessibility

Accessibility accounts for 42% of the county’s combined weighted risk score. No intertie appears in 15 of 34 assessed systems. Limited water sources is next, appearing in 10 of 34 assessed systems.

Indicator denominators range from 18 to 34 assessed systems.

Affordability

Affordability accounts for 12% of the county’s combined weighted risk score. Household socioeconomic burden appears in 8 of 34 assessed systems. Extreme water bill is next, appearing in 6 of 34 assessed systems.

Each indicator was assessed for 34 systems.

TMF Capacity

TMF Capacity accounts for 23% of the county’s combined weighted risk score. Total net annual income appears in 18 of 34 assessed systems. Operating ratio is next, appearing in 10 of 34 assessed systems.

Indicator denominators range from 31 to 34 assessed systems.

San Mateo County | Public water system SAFER profile
Data date: September 23, 2026
Page 3 of 3

Patterns and context

The countywide totals hide important differences among systems. The panels below show how SAFER status varies by system size and service-area economic status, what conditions appear among Failing systems, and how reported funding is distributed across the 36 systems in San Mateo County.

Status by system size

SAFER status within each population group

Among systems serving 500 people or fewer, 8 of 13 are Failing or At-Risk. This size group has the county’s highest concentration of high-concern classifications.

Economic context

Orange shows Failing or At-Risk systems within each service-area group

DAC and SDAC service areas contain 2 of 36 listed systems. Within those two groups, 2 systems are Failing or At-Risk.

Conditions among Failing systems

A system can appear under more than one condition

Frequently listed primary analytes

  • Total Haloacetic Acids (Haa5)1
  • Tthm1

Among 4 Failing systems, 2 report secondary MCL violation. The most frequently listed primary analytes are Total Haloacetic Acids (Haa5) and Tthm.

Reported funding

Totals since 2017 and number of systems reporting funding

No funding since 2017 is reported for systems in this county.

Key takeaways

25%

of systems are Failing or At-Risk

That represents 9 systems reporting service to 3,598 people. That is below the statewide average of 33%.

42%

of weighted risk comes from Accessibility

The most widespread individual flag is total net annual income, found in 18 of 34 assessed systems. Statewide, Accessibility accounts for 36% of weighted risk.

36%

of systems serve 500 people or fewer

Small systems account for 13 of the county’s 36 listed systems. That is below the statewide average of 63%.