Community Water System · PWS CA4110010
Montara Water and Sanitary District
Operator location Montara, California - 45% of 11 violations are health-based (upper-third health share (> 23%)); surface water source; 6,078 served per SDWIS.
- 6,078
- People served (this PWS)
- 11
- EPA violations (this PWS)
- 5
- Health-based (this PWS)
- No PFAS
- UCMR5 (this PWS)
Montara Water and Sanitary District standing, low SDWIS violation third
45% of 11 recorded violations are health-based - upper-third health share (> 23%). Corpus terciles use 29,740 systems serving 500+ (the sitemap cohort). Health-based share 45% is upper-third health share (> 23%). UCMR5: UCMR5 tested, none detected. Population rank #6,756 of 29,740 among systems serving 500+.
The verdict
Montara Water and Sanitary District is in the lower third by violation count (11; lower-third violation load (≤ 21 violations)). A low count does not mean the system is unmonitored - monitoring and reporting violations still appear in SDWIS. Population served is large (6,078; larger served population (> 3,309)), so household exposure scale sits behind the violation mix. Health-based share is 45% - most of this ledger is MCL or treatment-technique exceedance. UCMR5 tested this system and reported no PFAS above the minimum reporting level.
- #6,756 of 29,740
- Population · /systems
- #594 of 1,701
- Population · CA
- 11
- Total EPA violations on record
- 45%
- Health-based (MCL / treatment failure)
Population ordinals match the sitemap cohort (systems serving 500+, population_served DESC). See methodology · corpus placement.
System Details
- System Type
- Community
- Owner Type
- Local
- Connections
- 1,698
- County
- San Mateo
- School/Daycare
- No
- MCL Violations
- 5
- Monitoring Violations
- 2
- Treatment Tech Violations
- 0
Violation History
Contaminant violations recorded by EPA.
| Contaminant | Category | Count | Latest |
|---|---|---|---|
| CYANIDE | MCL | 2 | 1996 |
| Nitrate | MR | 2 | 1996 |
| Nitrate | MCL | 2 | 2010 |
| Coliform (TCR) | MCL | 1 | 1996 |
Violation Count vs. the National Corpus
Montara Water and Sanitary District has 11 recorded EPA violations, 19% of the 29,740 public water systems serving 500+ people nationwide carry fewer, and 79% carry more. 45% of this system's own violations are health-based (5 of 11), and it ranks #6,756 of 29,740 by population served among that same cohort.
EPA violations vs. the national water-system corpus
Public water systems serving 500+ people (EPA SDWIS)
11 Among the lowest violation counts fewer violations than 79% of 29,740 water systems
the national water-system corpus, bucketed by value
Each bar is a band; taller bars hold more water systems. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.
Source EPA SDWIS · 2026-05-15
PFAS Testing Results (UCMR5)
Results from EPA's Fifth Unregulated Contaminant Monitoring Rule. 0 of 203 samples detected PFAS.
| Contaminant | Date | Result | MRL | Status |
|---|---|---|---|---|
| PFTrDA | 8/12/2025 | <7.00 ppt | 7.00 ppt | Not Detected |
| NFDHA | 8/12/2025 | <20.00 ppt | 20.00 ppt | Not Detected |
| 9Cl-PF3ONS | 8/12/2025 | <2.00 ppt | 2.00 ppt | Not Detected |
| PFBA | 8/12/2025 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFHpS | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFTA | 8/12/2025 | <8.00 ppt | 8.00 ppt | Not Detected |
| PFBS | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFPeS | 8/12/2025 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFEESA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFPeA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFMPA | 8/12/2025 | <4.00 ppt | 4.00 ppt | Not Detected |
| 8:2 FTS | 8/12/2025 | <5.00 ppt | 5.00 ppt | Not Detected |
| 6:2 FTS | 8/12/2025 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFMBA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| ADONA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| NEtFOSAA | 8/12/2025 | <5.00 ppt | 5.00 ppt | Not Detected |
| 11Cl-PF3OUdS | 8/12/2025 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFUnA | 8/12/2025 | <2.00 ppt | 2.00 ppt | Not Detected |
| PFHxA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFDoA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFDA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFOA | 8/12/2025 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFOS | 8/12/2025 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFNA | 8/12/2025 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFHxS | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFHpA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| NMeFOSAA | 8/12/2025 | <6.00 ppt | 6.00 ppt | Not Detected |
| HFPO-DA | 8/12/2025 | <5.00 ppt | 5.00 ppt | Not Detected |
| 4:2 FTS | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFDA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| HFPO-DA | 8/12/2025 | <5.00 ppt | 5.00 ppt | Not Detected |
| ADONA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| 9Cl-PF3ONS | 8/12/2025 | <2.00 ppt | 2.00 ppt | Not Detected |
| 11Cl-PF3OUdS | 8/12/2025 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFUnA | 8/12/2025 | <2.00 ppt | 2.00 ppt | Not Detected |
| PFBA | 8/12/2025 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFDoA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFOA | 8/12/2025 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFOS | 8/12/2025 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFNA | 8/12/2025 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFHxA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFHxS | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| 4:2 FTS | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| 8:2 FTS | 8/12/2025 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFMPA | 8/12/2025 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFMBA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFEESA | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
| NFDHA | 8/12/2025 | <20.00 ppt | 20.00 ppt | Not Detected |
| PFPeS | 8/12/2025 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFHpS | 8/12/2025 | <3.00 ppt | 3.00 ppt | Not Detected |
Health-based violations on Montara Water and Sanitary District
5 health-based rows in the tables above map to MCL or treatment-technique exceedances, verify each contaminant code on the federal SDWIS report for CA4110010.
Sources: EPA SDWIS · California State Water Resources Control Board, Division of Drinking Water
Nationwide peers
11 violations · 6,078 served: nearest cross-state SDWIS matches.
Cross-state systems with similarly light violation ledgers
Nearest cross-state community systems (500+ served) by total SDWIS violations on record.
Cross-state systems with similar served population
Nearest cross-state systems by EPA SDWIS population_served (same 500+ sitemap gate).
What to do with Montara Water and Sanitary District
Use this system's EPA-reported record as a starting filter, not a final verdict.
- See how every tracked system in California compares on the same EPA violation measures. California systems
- Check whether PFAS was detected at this system under UCMR5 testing. PFAS guide
- Find and compare another public water system by name or PWSID. Search systems
EPA SDWIS and UCMR5 figures are informational only, not a substitute for a certified lab test of your own tap water.