PATTERSON, CA · Stanislaus County

WESTERN HILLS WATER DISTRICT/DIABLO GRAN Water System

Current status

No open violations on record as of July 4, 2026.

This system's next federally required Consumer Confidence Report is due July 1, 2027, under the EPA's revised reporting rule.

Data sourced from the EPA ECHO database (SDWA bulk download), last refreshed July 4, 2026. This is a record-keeping and public-information tool — it does not replace California’s official records. Always confirm current status with California before making decisions based on this information.

System facts

System ID (PWSID): CA5010039
System type: Community Water System
Population served: 2,000
Service connections: 596
Ownership: local government
Water source: surface water (rivers, lakes, or reservoirs)

Violation history

Follow-up Or Routine LCR Tap M/R
—
Lead and Copper Rule
January 1, 2018 – March 16, 2021
Resolved
Maximum Contaminant Level Violation, Average
Health-based
TTHM
October 1, 2016 – December 31, 2016
Resolved
Monitoring and Reporting (DBP)
—
CARBON, TOTAL
October 1, 2009 – December 31, 2009
Resolved
Consumer Confidence Report Complete Failure to Report
—
Consumer Confidence Rule
July 1, 2009 – July 2, 2009
Resolved
Maximum Contaminant Level Violation, Average
Health-based
TTHM
January 1, 2009 – March 31, 2009
Resolved
Monitoring, Routine Major (TCR)
—
Coliform (TCR)
June 1, 2008 – June 30, 2008
Resolved
Maximum Contaminant Level Violation, Average
Health-based
TTHM
April 1, 2008 – June 30, 2008
Resolved
Maximum Contaminant Level Violation, Average
Health-based
TTHM
July 1, 2007 – September 30, 2007
Resolved
Maximum Contaminant Level Violation, Average
Health-based
TTHM
January 1, 2006 – March 31, 2006
Resolved
Maximum Contaminant Level Violation, Average
Health-based
TTHM
July 1, 2005 – September 30, 2005
Resolved
Maximum Contaminant Level Violation, Average
Health-based
Total Haloacetic Acids (HAA5)
July 1, 2005 – September 30, 2005
Resolved
Maximum Contaminant Level Violation, Average
Health-based
Total Haloacetic Acids (HAA5)
April 1, 2005 – June 30, 2005
Resolved
Maximum Contaminant Level Violation, Average
Health-based
TTHM
January 1, 2005 – March 31, 2005
Resolved
Maximum Contaminant Level Violation, Average
Health-based
Total Haloacetic Acids (HAA5)
October 1, 2004 – December 31, 2004
Resolved

Resolved addressed and confirmed by the state

Period	Violation	Contaminant / rule	Health-based	Status
January 1, 2018 – March 16, 2021	Follow-up Or Routine LCR Tap M/R	Lead and Copper Rule	—	Resolved
October 1, 2016 – December 31, 2016	Maximum Contaminant Level Violation, Average	TTHM	Health-based	Resolved
October 1, 2009 – December 31, 2009	Monitoring and Reporting (DBP)	CARBON, TOTAL	—	Resolved
July 1, 2009 – July 2, 2009	Consumer Confidence Report Complete Failure to Report	Consumer Confidence Rule	—	Resolved
January 1, 2009 – March 31, 2009	Maximum Contaminant Level Violation, Average	TTHM	Health-based	Resolved
June 1, 2008 – June 30, 2008	Monitoring, Routine Major (TCR)	Coliform (TCR)	—	Resolved
April 1, 2008 – June 30, 2008	Maximum Contaminant Level Violation, Average	TTHM	Health-based	Resolved
July 1, 2007 – September 30, 2007	Maximum Contaminant Level Violation, Average	TTHM	Health-based	Resolved
January 1, 2006 – March 31, 2006	Maximum Contaminant Level Violation, Average	TTHM	Health-based	Resolved
July 1, 2005 – September 30, 2005	Maximum Contaminant Level Violation, Average	TTHM	Health-based	Resolved
July 1, 2005 – September 30, 2005	Maximum Contaminant Level Violation, Average	Total Haloacetic Acids (HAA5)	Health-based	Resolved
April 1, 2005 – June 30, 2005	Maximum Contaminant Level Violation, Average	Total Haloacetic Acids (HAA5)	Health-based	Resolved
January 1, 2005 – March 31, 2005	Maximum Contaminant Level Violation, Average	TTHM	Health-based	Resolved
October 1, 2004 – December 31, 2004	Maximum Contaminant Level Violation, Average	Total Haloacetic Acids (HAA5)	Health-based	Resolved

Resolved addressed and confirmed by the state

Enforcement actions

July 16, 2019State Compliance achieved1 linked violation
July 16, 2019State Compliance achieved1 linked violation
October 19, 2018State Administrative/Compliance Order without penalty issued1 linked violation
May 10, 2018State Compliance achieved7 linked violations
November 1, 2016State Compliance achieved1 linked violation
October 1, 2016State Administrative/Compliance Order without penalty issued1 linked violation
April 30, 2016State Compliance achieved1 linked violation
February 3, 2016State Administrative/Compliance Order without penalty issued1 linked violation
October 23, 2014State Administrative/Compliance Order without penalty issued7 linked violations
March 31, 2010State Compliance achieved24 linked violations
June 23, 2009State Compliance achieved1 linked violation
August 23, 2005State Compliance achieved4 linked violations
December 30, 2004State Compliance achieved2 linked violations
November 30, 2004State Compliance achieved1 linked violation

Contact

KOVICH, MARK

408-396-2511

PATTERSON, CA 95363