MARIN MUNICIPAL WATER DISTRICT Water Quality Report
Serving roughly 186,895 people in Marin County, California.
Data current as of July 2026
🔍Straight from EPA
🧪Real Lab Results
📅Updated Quarterly
🏠Local Expertise
Results for MARIN MUNICIPAL WATER DISTRICT
1 water provider directly on file, serving roughly 186,895 people in Marin County, California.
Quick answer: MARIN MUNICIPAL WATER DISTRICT has no violations on file. One reading is worth knowing about: Magnesium was measured at 14MG/L, among the highest of the 103 providers on file in this area. It's the most notable figure in this system's record among its 103 local peers.
Lead Summary
Totalhaloaceticacids (HAA5)
TTHM
Chloroform
Bromodichloromethane
Dibromochloromethane
Dichloroaceticacid
Trichloroaceticacid
Dibromoaceticacid
Aggressive Index
Temperature (CENTIGRADE)
Langelier Index (Source Temp.)
Orthophosphate
Carbon, Total
Magnesium
Potassium
Sodium
Calcium
Alkalinity, Total
Alkalinity, Bicarbonate
Hardness, Total (ASCACO3)
TDS
Chloride
Sulfate
Fluoride
Nitrate
Nitrate-Nitrite
Radon
pH
Chromium, Hex
Chlorate
Zinc
Conductivity (at 25°C)
Utility MARIN MUNICIPAL WATER DISTRICTPopulation served 186,895Owner Local government
No violations on file
Contaminants found
Metals
Naturally occurring or corrosion-related elements, e.g. lead, arsenic, copper
Lead Summary
Detected: 0 mg/L (ppm)
12/31/2021
Chromium, Hex
Detected: 0.37 UG/L (ppb)
4/22/2025
Zinc
Detected: 180 UG/L (ppb)
10/6/2025
Disinfection Byproducts
Formed when chlorine used to disinfect water reacts with organic matter
Totalhaloaceticacids (HAA5)
Detected: 10 UG/L (ppb)
8/11/2025
TTHM
Detected: 21 UG/L (ppb)
8/11/2025
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: 10 UG/L (ppb)
8/11/2025
One of the individual trihalomethane disinfection byproducts, formed when chlorine reacts with organic matter.
Bromodichloromethane
Detected: 6.9 UG/L (ppb)
8/11/2025
Dibromochloromethane
Detected: 3.8 UG/L (ppb)
8/11/2025
Inorganics
Common dissolved minerals and salts, e.g. nitrate, fluoride, chloride
Chloride
Detected: 7.4 MG/L (ppm)
10/6/2025
Sulfate
Detected: 12 MG/L (ppm)
10/6/2025
Fluoride
Detected: 0.68 MG/L (ppm)
10/6/2025
Often added deliberately for dental health; can also occur naturally.
Nitrate
Detected: 0.43 MG/L (ppm)
1/14/2025
Commonly from agricultural fertilizer runoff or septic systems. Above the legal limit, it's an immediate concern especially for infants.
Nitrate-Nitrite
Detected: 0.43 MG/L (ppm)
1/14/2025
Minerals
Everyday minerals that mainly affect taste and water hardness
Magnesium
Detected: 14 MG/L (ppm)
10/6/2025
Potassium
Detected: 1.1 MG/L (ppm)
4/22/2025
Sodium
Detected: 20 MG/L (ppm)
10/6/2025
Calcium
Detected: 21 MG/L (ppm)
10/6/2025
Properties
General water characteristics like pH, hardness, and cloudiness (turbidity)
Orthophosphate
Detected: 0.3 MG/L (ppm)
10/6/2025
Hardness, Total (ASCACO3)
Detected: 110 MG/L (ppm)
10/6/2025
pH
Detected: 8.2 PH
10/6/2025
A measure of how acidic or basic the water is (7 is neutral). Affects taste and plumbing, not a direct health measure.
Calculated Parameters
Values worked out mathematically from other test results, not measured directly
Alkalinity, Bicarbonate
Detected: 120 MG/L (ppm)
10/6/2025
Other
Additional substances tested that don't fit neatly into the categories above
Dichloroaceticacid
Detected: 5.8 UG/L (ppb)
8/11/2025
Trichloroaceticacid
Detected: 3.5 UG/L (ppb)
8/11/2025
Dibromoaceticacid
Detected: 1.1 UG/L (ppb)
8/11/2025
Aggressive Index
Detected: 11.48 AGGR
8/28/2025
Temperature (CENTIGRADE)
Detected: 22.4 C
8/28/2025
Langelier Index (Source Temp.)
Detected: -0.34 LANG
8/28/2025
Carbon, Total
Detected: 0.715 MG/L (ppm)
10/6/2025
Alkalinity, Total
Detected: 120 MG/L (ppm)
10/6/2025
TDS
Detected: 150 MG/L (ppm)
10/6/2025
Radon
Detected: 78.4 PCI/L
4/23/2025
Chlorate
Detected: 37 UG/L (ppb)
10/6/2025
Conductivity (at 25°C)
Detected: 290 UMHO/CM
10/6/2025
Filtration considerations: See the table below for how whole-house carbon, under-sink reverse osmosis, and under-sink carbon systems compare against what's actually on file here. These are general system types, not a specific product recommendation.