Water Quality: Hollister, CA
21 water systems • 53,795 people served
Multiple Health ViolationsWater Quality Summary
Hollister is served by 21 public water systems with a combined service population of 53,795 people, and has 107 EPA Safe Drinking Water Act violations on record. Critically, 38 of those are health-based violations, meaning one or more contaminants were detected above EPA-established safe levels — a serious public health concern. Hollister's violation count is 123% above the national average for California. Contaminants associated with violations include Barium, Contaminant 2920, Gross Alpha, Haloacetic Acids, Nitrate-Nitrite.
Contaminants Found
Increases blood pressure and causes cardiovascular effects with long-term exposure.
Common source: Natural rock deposits, oil drilling operations, coal power plant waste
EPA limit: 2 mg/L
Alpha-emitting radioactive particles increase cancer risk, particularly from bone and other internal cancers.
Common source: Natural uranium and radium in geological formations
EPA limit: 15 pCi/L (excluding radon and uranium)
Linked to increased cancer risk and potential reproductive and developmental effects with long-term exposure.
Common source: Reaction of chlorine disinfectants with organic matter in treated water
EPA limit: 0.060 mg/L (60 ppb)
Causes methemoglobinemia in infants and may pose cancer risks with long-term exposure.
Common source: Fertilizer runoff, septic systems, animal feedlots, natural deposits
EPA limit: 10 mg/L (as nitrogen)
Trihalomethanes and haloacetic acids that increase cancer risk and may cause adverse reproductive outcomes.
Common source: Chlorine disinfection reacting with natural organic matter in source water
EPA limit: TTHM: 0.080 mg/L; HAA5: 0.060 mg/L
Total trihalomethanes are linked to increased risk of bladder cancer and adverse reproductive outcomes.
Common source: Reaction of chlorine disinfectants with naturally occurring organic matter in water
EPA limit: 0.080 mg/L (80 ppb)
Water Systems Serving Hollister
| System Name | PWSID | Source | Population | Violations |
|---|---|---|---|---|
| HOLLISTER, CITY OF | CA3510001 | Surface Water | 26,017 | 25 |
| SUNNYSLOPE COUNTY WATER DIST | CA3510003 | Surface Water | 24,954 | 0 |
| RANCHO SAN JOAQUIN MWC | CA3500581 | Groundwater | 914 | 14 |
| CASA DE FRUTA WATER SYSTEM | CA4300611 | Groundwater | 250 | 3 |
| CSA NO. 31 STONEGATE WS | CA3500006 | Surface Water | 230 | 10 |
| SAN JUSTO MUTUAL WATER COMPANY | CA3500550 | Groundwater | 160 | 9 |
| HOLLISTER RANCH ESTATES | CA3500904 | Groundwater | 150 | 15 |
| ROSA MORADA MUTUAL WATER COMPANY | CA3500549 | Groundwater | 138 | 2 |
| ASHFORD HIGHLANDS MWC | CA3500900 | Groundwater | 132 | 0 |
| DUNNEVILLE ESTATES CSA #50 | CA3500910 | Groundwater | 120 | 0 |
| MCMAHON ROAD MUTUAL WATER COMPANY | CA3500510 | Groundwater | 102 | 1 |
| COMSTOCK MUTUAL WATER COMPANY | CA3500912 | Groundwater | 100 | 0 |
| UNION HEIGHTS MWC | CA3500825 | Groundwater | 98 | 1 |
| VINEYARD ESTATES MWC | CA3500579 | Groundwater | 90 | 6 |
| CREEKBRIDGE MUTUAL WATER COMPANY | CA3500911 | Groundwater | 69 | 0 |
| VALENZUELA WATER SYSTEM | CA3500527 | Groundwater | 55 | 14 |
| CASA DE FRUTA ORCHARDS | CA3500511 | Groundwater | 53 | 1 |
| VENTURE ESTATES MWC | CA3500552 | Groundwater | 50 | 1 |
| SPRINGWOOD ESTATES MWC | CA3500575 | Groundwater | 50 | 1 |
| WHISPERING PINES INN | CA3500810 | Groundwater | 38 | 4 |
| SAN BENITO COUNTY WATER DISTRICT | CA3510007 | Surface Water | 25 | 0 |
Concerned About Your Water?
A home water filter can remove common contaminants. NSF-certified filters are tested against EPA standards.
Consider a reverse osmosis system for comprehensive filtration or a carbon filter for basic improvement.
Other Cities in California
Data Sources
Drinking water violation data from the EPA Safe Drinking Water Information System (SDWIS). Data includes all recorded violations for active community water systems.