Community Water System · PWS CA4110011
Coastside County Water District
Operator location Half Moon Bay, California - 42% of 33 violations are health-based (upper-third health share (> 23%)); surface water source; 18,940 served per SDWIS.
- 18,940
- People served (this PWS)
- 33
- EPA violations (this PWS)
- 14
- Health-based (this PWS)
- No PFAS
- UCMR5 (this PWS)
Coastside County Water District standing, mid SDWIS violation third
42% of 33 recorded violations are health-based - upper-third health share (> 23%). Corpus terciles use 29,740 systems serving 500+ (the sitemap cohort). Health-based share 42% is upper-third health share (> 23%). UCMR5: UCMR5 tested, none detected. Population rank #2,846 of 29,740 among systems serving 500+.
The verdict
Coastside County Water District lands in the middle third by violation volume (33), large enough for peer comparisons without matching the fleet's heaviest ledgers. Population served is large (18,940; larger served population (> 3,309)), so household exposure scale sits behind the violation mix. Health-based share is 42% - most of this ledger is MCL or treatment-technique exceedance. UCMR5 tested this system and reported no PFAS above the minimum reporting level.
- #2,846 of 29,740
- Population · /systems
- #362 of 1,701
- Population · CA
- 33
- Total EPA violations on record
- 42%
- 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
- 6,617
- County
- San Mateo
- School/Daycare
- No
- MCL Violations
- 10
- Monitoring Violations
- 16
- Treatment Tech Violations
- 4
Violation History
Contaminant violations recorded by EPA.
| Contaminant | Category | Count | Latest |
|---|---|---|---|
| Coliform (TCR) | MCL | 10 | 2004 |
| Nitrate | MR | 8 | 2001 |
| Coliform (TCR) | MR | 6 | 2003 |
| Surface Water Treatment Rule | TT | 4 | 2008 |
| Coliform (TCR) | Other | 2 | 1996 |
| Surface Water Treatment Rule | MR | 1 | 2005 |
| Lead and Copper Rule | MR | 1 | 1993 |
Violation Count vs. the National Corpus
Coastside County Water District has 33 recorded EPA violations, 45% of the 29,740 public water systems serving 500+ people nationwide carry fewer, and 54% carry more. 42% of this system's own violations are health-based (14 of 33), and it ranks #2,846 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)
33 Lower than most fewer violations than 54% 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 232 samples detected PFAS.
| Contaminant | Date | Result | MRL | Status |
|---|---|---|---|---|
| PFNA | 9/11/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFPeS | 9/11/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFHpS | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFHpA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| NFDHA | 9/11/2024 | <20.00 ppt | 20.00 ppt | Not Detected |
| PFOA | 9/11/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFTA | 9/11/2024 | <8.00 ppt | 8.00 ppt | Not Detected |
| PFTrDA | 9/11/2024 | <7.00 ppt | 7.00 ppt | Not Detected |
| NEtFOSAA | 9/11/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFBS | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFHxS | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFOS | 9/11/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFDA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFDoA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFHxA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFMBA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| NMeFOSAA | 9/11/2024 | <6.00 ppt | 6.00 ppt | Not Detected |
| PFEESA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFUnA | 9/11/2024 | <2.00 ppt | 2.00 ppt | Not Detected |
| PFPeA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFMPA | 9/11/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| 8:2 FTS | 9/11/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| 4:2 FTS | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| 6:2 FTS | 9/11/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFBA | 9/11/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| HFPO-DA | 9/11/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| ADONA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| 9Cl-PF3ONS | 9/11/2024 | <2.00 ppt | 2.00 ppt | Not Detected |
| 11Cl-PF3OUdS | 9/11/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFHxA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFMBA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFPeA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFMPA | 9/11/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| 8:2 FTS | 9/11/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| 4:2 FTS | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| 6:2 FTS | 9/11/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| PFBA | 9/11/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| HFPO-DA | 9/11/2024 | <5.00 ppt | 5.00 ppt | Not Detected |
| ADONA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| 9Cl-PF3ONS | 9/11/2024 | <2.00 ppt | 2.00 ppt | Not Detected |
| PFEESA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFUnA | 9/11/2024 | <2.00 ppt | 2.00 ppt | Not Detected |
| PFTA | 9/11/2024 | <8.00 ppt | 8.00 ppt | Not Detected |
| PFDoA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFDA | 9/11/2024 | <3.00 ppt | 3.00 ppt | Not Detected |
| PFOA | 9/11/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFOS | 9/11/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
| PFTrDA | 9/11/2024 | <7.00 ppt | 7.00 ppt | Not Detected |
| NMeFOSAA | 9/11/2024 | <6.00 ppt | 6.00 ppt | Not Detected |
| PFNA | 9/11/2024 | <4.00 ppt | 4.00 ppt | Not Detected |
Health-based violations on Coastside County Water District
14 health-based rows in the tables above map to MCL or treatment-technique exceedances, verify each contaminant code on the federal SDWIS report for CA4110011.
Sources: EPA SDWIS · California State Water Resources Control Board, Division of Drinking Water
Nationwide peers
33 violations · 18,940 served: nearest cross-state SDWIS matches.
Cross-state systems near this violation count
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 Coastside County Water 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.