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Results for Marin County, CA

103 water providers on file for this county, sorted by population served.

Quick answer: Marin County has 103 water providers profiled, sorted by population served.

Lead Summary
Copper Summary
Copper, Free
Nitrate
Gross Alpha Particle Activity
Iron
Chromium, Hex
Totalhaloaceticacids (HAA5)
TTHM
Chloroform
Bromodichloromethane
Dibromochloromethane
Dichloroaceticacid
Trichloroaceticacid
Manganese
Lead
Bromoform
Dibromoaceticacid
Carbon, Total
Aggressive Index
Temperature (CENTIGRADE)
Langelier Index (Source Temp.)
Orthophosphate
Magnesium
Potassium
Sodium
Calcium
Alkalinity, Total
Alkalinity, Bicarbonate
Hardness, Total (ASCACO3)
TDS
Chloride
Sulfate
Fluoride
Nitrate-Nitrite
Radon
pH
Chlorate
Zinc
Conductivity (at 25°C)
Arsenic
Monobromoaceticacid
Turbidity
Odor
Color
Lithium
Radium-228
Combined Radium (-226 & -228)
Chromium
Aluminum
pH, Field
Boron, Total
Nickel
Selenium
Monochloroaceticacid
Barium
Bromate
Toluene
Antimony, Total

Violations on file

Lead And Copper Rule Revisions

Currently open health violation

Found at 2 of 103 providers

Contaminants found

Metals

Naturally occurring or corrosion-related elements, e.g. lead, arsenic, copper

Lead Summary

Detected: 0.01 mg/L (ppm)

Found at 25 providers

Copper Summary

Detected: 2.9 mg/L (ppm)

Found at 11 providers

Copper, Free

Detected: 200 UG/L (ppb)

Found at 8 providers

Iron

Detected: 1800 UG/L (ppb)

Found at 7 providers

Mostly an aesthetic issue (metallic taste, staining) rather than a health concern at typical levels.

Chromium, Hex

Detected: 1.5 UG/L (ppb)

Found at 13 providers

Manganese

Detected: 650 UG/L (ppb)

Found at 7 providers

Mainly a taste/staining concern at typical levels; long-term neurological research at high chronic exposure is ongoing.

Lead

Detected: 38 UG/L (ppb)

Found at 2 providers

A metal that can leach from old pipes, solder, and fixtures. Current medical guidance holds there is no truly safe level of lead exposure, especially for children and pregnant women.

Zinc

Detected: 180 UG/L (ppb)

Found at 2 providers

Arsenic

Detected: 4.3 UG/L (ppb)

Found at 7 providers

Occurs naturally in some groundwater. Long-term exposure above the legal limit (10 ppb) has been linked to increased cancer risk and cardiovascular disease.

Chromium

Detected: 3.9 UG/L (ppb)

Found at 4 providers

Occurs in two forms — trivalent (an essential nutrient in trace amounts) and hexavalent (linked to increased cancer risk).

Aluminum

Detected: 1500 UG/L (ppb)

Found at 2 providers

Nickel

Detected: 4.2 UG/L (ppb)

7/9/2025

Selenium

Detected: 2.1 UG/L (ppb)

7/9/2025

Barium

Detected: 110 UG/L (ppb)

6/16/2025

Antimony, Total

Detected: 9.5 UG/L (ppb)

8/26/2025

Disinfection Byproducts

Formed when chlorine used to disinfect water reacts with organic matter

Totalhaloaceticacids (HAA5)

Detected: 41 UG/L (ppb)

Found at 15 providers

TTHM

Detected: 54 UG/L (ppb)

Found at 17 providers

A group of disinfection byproducts formed when chlorine reacts with organic matter. Long-term exposure above the legal limit has been linked to increased cancer risk in some studies.

Chloroform

Detected: 31 UG/L (ppb)

Found at 14 providers

One of the individual trihalomethane disinfection byproducts, formed when chlorine reacts with organic matter.

Bromodichloromethane

Detected: 17 UG/L (ppb)

Found at 17 providers

Dibromochloromethane

Detected: 20 UG/L (ppb)

Found at 17 providers

Bromoform

Detected: 11 UG/L (ppb)

Found at 13 providers

Inorganics

Common dissolved minerals and salts, e.g. nitrate, fluoride, chloride

Nitrate

Detected: 5.2 MG/L (ppm)

Found at 14 providers

Commonly from agricultural fertilizer runoff or septic systems. Above the legal limit, it's an immediate concern especially for infants.

Chloride

Detected: 86 MG/L (ppm)

Found at 6 providers

Sulfate

Detected: 53 MG/L (ppm)

Found at 6 providers

Fluoride

Detected: 0.68 MG/L (ppm)

Found at 8 providers

Often added deliberately for dental health; can also occur naturally.

Nitrate-Nitrite

Detected: 1.1 MG/L (ppm)

Found at 2 providers

Boron, Total

Detected: 65 UG/L (ppb)

9/16/2025

Minerals

Everyday minerals that mainly affect taste and water hardness

Magnesium

Detected: 14 MG/L (ppm)

Found at 8 providers

Potassium

Detected: 1.9 MG/L (ppm)

Found at 2 providers

Sodium

Detected: 58 MG/L (ppm)

Found at 8 providers

Calcium

Detected: 39 MG/L (ppm)

Found at 6 providers

Properties

General water characteristics like pH, hardness, and cloudiness (turbidity)

Gross Alpha Particle Activity

Detected: 2.43 PCI/L

Found at 5 providers

Orthophosphate

Detected: 0.5 MG/L (ppm)

Found at 2 providers

Hardness, Total (ASCACO3)

Detected: 120 MG/L (ppm)

Found at 6 providers

Detected: 8.2 PH

Found at 6 providers

A measure of how acidic or basic the water is (7 is neutral). Affects taste and plumbing, not a direct health measure.

pH, Field

Detected: 7.65 PH

9/17/2025

PFAS & Emerging Contaminants

Human-made "forever chemicals" and other substances not yet fully regulated

Lithium

Detected: 10.2 µg/L (ppb)

12/6/2023

Occurs naturally in some groundwater. Not currently federally regulated in drinking water.

Petroleum Compounds

Substances associated with fuel or petroleum contamination

Toluene

Detected: 49 UG/L (ppb)

9/30/2025

Calculated Parameters

Values worked out mathematically from other test results, not measured directly

Alkalinity, Bicarbonate

Detected: 120 MG/L (ppm)

Found at 6 providers

Other

Additional substances tested that don't fit neatly into the categories above

Dichloroaceticacid

Detected: 21 UG/L (ppb)

Found at 15 providers

Trichloroaceticacid

Detected: 8.7 UG/L (ppb)

Found at 12 providers

Dibromoaceticacid

Detected: 6.9 UG/L (ppb)

Found at 17 providers

Carbon, Total

Detected: 2.06 MG/L (ppm)

Found at 3 providers

Aggressive Index

Detected: 11.48 AGGR

Found at 2 providers

Temperature (CENTIGRADE)

Detected: 22.4 C

Found at 2 providers

Langelier Index (Source Temp.)

Detected: -0.34 LANG

Found at 2 providers

Alkalinity, Total

Detected: 120 MG/L (ppm)

Found at 6 providers

TDS

Detected: 270 MG/L (ppm)

Found at 6 providers

Radon

Detected: 78.4 PCI/L

4/23/2025

Chlorate

Detected: 37 UG/L (ppb)

10/6/2025

Conductivity (at 25°C)

Detected: 490 UMHO/CM

Found at 6 providers

Monobromoaceticacid

Detected: 1.4 UG/L (ppb)

Found at 3 providers

Turbidity

Detected: 70 NTU

Found at 4 providers

A measure of water cloudiness from suspended particles.

Odor

Detected: 35 TON

Found at 3 providers

Color

Detected: 200 UNITS

Found at 5 providers

Radium-228

Detected: 0.889 PCI/L

Found at 3 providers

Combined Radium (-226 & -228)

Detected: 1.19 PCI/L

Found at 2 providers

A naturally occurring radioactive element found in some groundwater.

Monochloroaceticacid

Detected: 3.2 UG/L (ppb)

9/4/2025

Bromate

Detected: 5.9 UG/L (ppb)

10/9/2025

Filtration considerations: General system types, not a specific product recommendation.

Contaminant	Whole-House Carbon	Under-Sink RO	Under-Sink Carbon
Total Trihalomethanes (TTHM)	Yes	Yes	Yes
Haloacetic Acids (HAA5)	Yes	Yes	Yes
Chloroform	Yes	Yes	Yes
Chlorine / Taste	Yes	Yes	Yes
Sediment / Turbidity	Yes	Yes	Yes
Trichloroethylene	Yes	Yes	Yes
Tetrachloroethylene	Yes	Yes	Yes
cis-1,2-Dichloroethylene	Yes	Yes	Yes
1,1-Dichloroethylene	Yes	Yes	Yes
Bromoform	Yes	Yes	Yes
Bromodichloromethane	Yes	Yes	Yes
Dibromochloromethane	Yes	Yes	Yes
1,1,2-Trichloroethane	Yes	Yes	Yes
Vinyl Chloride	Yes	Yes	Yes
Carbon Tetrachloride	Yes	Yes	Yes
Benzene	Yes	Yes	Yes
Toluene	Yes	Yes	Yes
Xylene	Yes	Yes	Yes
Totalhaloaceticacids (HAA5)	Yes	Yes	Yes
Lead	Partial	Yes	Partial
Arsenic	Partial	Yes	Partial
Chromium-6 (Hexavalent)	Partial	Yes	Partial
Copper	Partial	Yes	Partial
Combined Uranium	Partial	Yes	Partial
PFOA	Partial	Yes*	Partial
PFOS	Partial	Yes*	Partial
Nitrate	Partial	Yes	Partial
Combined Radium	Partial	Yes	Partial
Copper, Free	Partial	Yes	Partial
Iron	Partial	Yes	Partial
Chromium, Hex	Partial	Yes	Partial
Dichloroaceticacid	Partial	Yes	Partial
Trichloroaceticacid	Partial	Yes	Partial
Manganese	Partial	Yes	Partial
Dibromoaceticacid	Partial	Yes	Partial
Carbon, Total	Partial	Yes	Partial
Aggressive Index	Partial	Yes	Partial
Temperature (CENTIGRADE)	Partial	Yes	Partial
Langelier Index (Source Temp.)	Partial	Yes	Partial
Alkalinity, Total	Partial	Yes	Partial
TDS	Partial	Yes	Partial
Chloride	Partial	Yes	Partial
Sulfate	Partial	Yes	Partial
Fluoride	Partial	Yes	Partial
Nitrate-Nitrite	Partial	Yes	Partial
Radon	Partial	Yes	Partial
Chlorate	Partial	Yes	Partial
Zinc	Partial	Yes	Partial
Conductivity (at 25°C)	Partial	Yes	Partial
Monobromoaceticacid	Partial	Yes	Partial
Odor	Partial	Yes	Partial
Color	Partial	Yes	Partial
Lithium	Partial	Yes*	Partial
Combined Radium (-226 & -228)	Partial	Yes	Partial
Chromium	Partial	Yes	Partial
Aluminum	Partial	Yes	Partial
Boron, Total	Partial	Yes	Partial
Nickel	Partial	Yes	Partial
Selenium	Partial	Yes	Partial
Monochloroaceticacid	Partial	Yes	Partial
Barium	Partial	Yes	Partial
Bromate	Partial	Yes	Partial
Antimony, Total	Partial	Yes	Partial
Coliform Bacteria (indicator)	No	Yes	No
Gross Alpha Particle Activity	No	No	No
Orthophosphate	No	No	No
Magnesium	No	Partial	No
Potassium	No	Partial	No
Sodium	No	Partial	No
Calcium	No	Partial	No
Alkalinity, Bicarbonate	No	No	No
Hardness, Total (ASCACO3)	No	No	No
pH	No	No	No
pH, Field	No	No	No

Individual water providers

MARIN MUNICIPAL WATER DISTRICT No violations on file — pop. 186,895
NORTH MARIN WATER DISTRICT No violations on file — pop. 61,691
NPS GGNRA No violations on file — pop. 18,447
BOLINAS COMMUNITY PUD No violations on file — pop. 2,483
LARRY BASS No violations on file — pop. 2,000
LARRY BASS No violations on file — pop. 2,000
NORTH MARIN WD - PT. REYES No violations on file — pop. 1,841
CSP - ANGEL ISLAND ST PARK No violations on file — pop. 1,622
NPS PRNS - BEACHES No violations on file — pop. 1,560
INVERNESS PUBLIC UTILITY DIST No violations on file — pop. 1,445
NPS PRNS - LIGHTHOUSE No violations on file — pop. 1,202
NPS PRNS - GLEN AND WILDCAT CAMPGROUNDS No violations on file — pop. 1,200

LAWSON S LANDING No violations on file — pop. 946
STINSON BEACH COUNTY WTR DIST No violations on file — pop. 583
CSP - MT TAM THEATRE WELL No violations on file — pop. 504
CSP - TOMALES BAY ST PARK No violations on file — pop. 503
LAWSONS LANDING No violations on file — pop. 500
ELK CREEK COMMUNITY SERVICES D No violations on file — pop. 450
TOMALES HIGH SCHOOL Open violation — pop. 427
FAIRVIEW SCHOOL No violations on file — pop. 391
COAST SPRINGS - CAL. WATER SERVICE (PUC) No violations on file — pop. 388
NPS PRNS - FIVE BROOKS No violations on file — pop. 365
WILLIAM G LANDRY No violations on file — pop. 340
MUIR BEACH COMMUNITY No violations on file — pop. 336
NPS PRNS - LAGUNA SYSTEM No violations on file — pop. 316
CSP - SAMUEL TAYLOR ST PARK No violations on file — pop. 310
PAUL BRINGGS No violations on file — pop. 300
SKYWALKER RANCH No violations on file — pop. 250
TOMALES ELEM & MIDDLE SCHOOL No violations on file — pop. 225
WALKER CREEK RANCH EDUCATIONAL CENTER No violations on file — pop. 212
ESTERO MUTUAL No violations on file — pop. 206
DOMINICAN COLLEGE No violations on file — pop. 200
NPS PRNS - FIVE BROOKS No violations on file — pop. 200
JAKC HELVIE No violations on file — pop. 200
NUNZIO FEMINO No violations on file — pop. 200
HOG ISLAND OYSTER CO. No violations on file — pop. 172
JUNCO MOIBLE HOME PARK No violations on file — pop. 165
MARCONI INCONFERENCE CENTER No violations on file — pop. 150
ARTOIS CSD No violations on file — pop. 150
MARIN FRENCH CHEESE CO No violations on file — pop. 143
PLASKETT RECREATIONAL AREA No violations on file — pop. 140
KANAWHA VILLAGE MHP No violations on file — pop. 125
OLLIE FRAZIER No violations on file — pop. 125
CSP - MARCONI CONFERENCE CENTER No violations on file — pop. 120
WILLIAM TELL HOUSE No violations on file — pop. 110
CHUCK HARRIS, SR No violations on file — pop. 108
NICASIO RANCH LLC No violations on file — pop. 104
TONY S SEAFOOD RESTAURANT No violations on file — pop. 103
CAMP TAMARANCHO No violations on file — pop. 101
ANGEL S CAFE No violations on file — pop. 100
BOTHIN YOUTH CENTER No violations on file — pop. 100
FLYING J No violations on file — pop. 100
CHUCK STOUT No violations on file — pop. 90
NICK'S COVE No violations on file — pop. 90
TOMALES TIN BUILDING No violations on file — pop. 82
BLACK BUTTE MOBILE HOME PARK No violations on file — pop. 75
CSP - MT TAM EAST PEAK SYSTEM No violations on file — pop. 75
NPS PRNS - SKY CAMP CAMPGROUND No violations on file — pop. 75
GREEN GULCH FARM Open violation — pop. 75
BAYLISS SCHOOL No violations on file — pop. 69
MCEVOY RANCH WATER SYSTEM No violations on file — pop. 66
SYNANON WALKER CREEK SETTLEMEN No violations on file — pop. 65
EUGENE UNRUH No violations on file — pop. 60
ARTOIS SCHOOL No violations on file — pop. 54
LAKE SCHOOL No violations on file — pop. 51
U.S. COAST GUARD - PT. REYES No violations on file — pop. 50
MARIE LACQUE No violations on file — pop. 50
GEORGE WARD No violations on file — pop. 50
MAIF - MARSHALL AQUA IMPROVEMENT FORUM No violations on file — pop. 50
TOMALES CHURCH OF THE ASSUMPTION No violations on file — pop. 50
MARSHALL BOAT WORKS No violations on file — pop. 50
ALL HANDS ECOLOGY No violations on file — pop. 50
AUDUBON CANYON RANCH - MGP VOLUNTEER No violations on file — pop. 50
DONNIE R WALKER No violations on file — pop. 49
WM G LOPACHUCK No violations on file — pop. 49
NICASIO SCHOOL No violations on file — pop. 48
SLIDE RANCH No violations on file — pop. 47
ANITA FERNANDEZ No violations on file — pop. 45
JOHN MADERIOUS No violations on file — pop. 40
NICASIO VALLEY RANCH MUTUAL No violations on file — pop. 36
BLUE MOUNTAIN CENTER No violations on file — pop. 35
BLUE GUM MOTEL No violations on file — pop. 32
KOA GREEN ACRES PARK No violations on file — pop. 30
ICE SPRINGS ADMINISTRATIVE SIT No violations on file — pop. 30
DRAKES BAY OYSTER COMPANY No violations on file — pop. 30
HERALD SMITH No violations on file — pop. 29
SHORELINE SCHOOL DIST: BUS GARAGE No violations on file — pop. 26
ALDER SPRINGS CENTER No violations on file — pop. 25
BOTHIN YOUTH CENTER No violations on file — pop. 25
MARSHALL TAVERN No violations on file — pop. 25
ALTA MIRA HOTEL No violations on file — pop. 25
NICASIO VALLEY RANCH MUTUAL WATER CO. No violations on file — pop. 25
BULLTAIL RANCH No violations on file — pop. 25
BLUE MOUNTAIN CENTER No violations on file — pop. 25
AUDUBON CANYON RANCH No violations on file — pop. 25
AUDUBON VOLUNTEER CANYON No violations on file — pop. 25
WAYNE DAVIS No violations on file — pop. 25
DEVILS GULCH RANCH WATER SYSTEM No violations on file — pop. 25
DIEKMANN'S GENERAL STORE No violations on file — pop. 25
DUCK COVE WATER SYSTEM No violations on file — pop. 12
GLENN COLUSA IRRIGATION DISTRICT No violations on file — pop. 11
JENSEN OYSTER COMPANY No violations on file — pop. 1
DE VOR NURSERIES No violations on file — pop. 0

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What is TTHM? Understanding EPA Violation Status Is Chromium-6 Dangerous? Whole-House vs. Under-Sink Filtration Lead and Copper in Drinking Water What is PFAS? Arsenic and Uranium Explained Nitrate and Fluoride Explained Water Hardness, pH, and Turbidity What is Coliform Bacteria?

Marin County, CA Water Quality Report

Violations on file

Contaminants found

Individual water providers