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WaterSafeCheck
Official EPA SDWIS Verified ReportWater Quality & Testing GuideStatus: Normal Operations

ZIP Code 94933 Water Quality & Testing Report

Forest Knolls, CA · Marin County County · Updated for 2026

Quick EPA Verified Answer

Is Tap Water Safe to Drink in ZIP 94933 (Forest Knolls, CA)?

Caution / Filtration Recommended: Tap water in ZIP code 94933 (Forest Knolls, CA) has compliance concerns, earning an EPA Safety Grade of C (65/100) due to 0 health violation(s) and 0 ppb lead. While treated by Marin Municipal Water District, residents are advised to use an NSF/ANSI 53 certified water filter for drinking and cooking.

Safety Score
C

Water Safety Grade

Fair — Some compliance concerns

Health Violations

0

Total Violations

0

Lead Risk

High

Contaminants

0

About Tap Water in ZIP Code 94933

Tap water in ZIP code 94933 (Forest Knolls, CA) is distributed by Marin Municipal Water District (EPA ID: CA2110002), serving approximately 186,895 residents. Based on EPA Safe Drinking Water Act compliance records, this system receives a water safety grade of C with a composite quality score of 65/100.

Water System

Marin Municipal Water District

EPA ID: CA2110002

Water Source

Surface Water

Population Served

186,895 residents

County

Marin County County, California

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Lead Levels in ZIP 94933

EPA action level: 15 ppb | Public health goal: 0 ppb

Lead Data Not Available

Lead testing data was not found in EPA records for ZIP code 94933. Contact Marin Municipal Water District to request lead testing results.

Lead exposure risk in 94933 is rated High. EPA models estimate a 68% exposure probability based on housing and infrastructure age.

Lead Exposure Risk Rating
High
Lead Exposure Probability

EPA model estimate based on housing age and infrastructure

68%
Note: Lead levels above are the 90th percentile from EPA monitoring — meaning 90% of samples were at or below this level. Even "undetected" tap water lead doesn't account for lead leaching from home plumbing. If your home was built before 1986, individual tap testing is recommended.
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Water Hardness & Mineral Content

Grains per gallon (GPG) & Parts per million (PPM / mg/L)

Classification: Hard8 GPG · 136 mg/L

Water in ZIP 94933 is Hard (136 mg/L / 8 GPG). Residents may notice white mineral spots on glassware, reduced soap efficiency, and mineral scale on faucets and showerheads.

Recommendation: An ion-exchange water softener or descaler is recommended to prolong the life of water heaters, dishwashers, and plumbing.
Hardness (GPG)

Grains per gallon

8 GPG
Hardness (PPM / mg/L)

Parts per million CaCO3

136 mg/L
Appliance Scaling Risk
High / Severe

Official EPA SDWIS Database Entry

Utility: Marin Municipal Water District · PWSID: CA2110002

Verify on EPA.gov
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Violation History

Past 5 years — EPA SDWIS data

Marin Municipal Water District has recorded zero violations in the EPA compliance database over the past 5 years.

Total Violations (5 yr)
0
Health-Based Violations
0
Unresolved Violations
0
Boil Water Advisories
0
Compliance Risk
Unknown
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Contaminants Detected

Contaminants with health-based violations on record

No health-based contaminant violations are on record for ZIP code 94933 under the Safe Drinking Water Act.

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Water Source & Environmental Factors

Surface Water

This system draws water from lakes, rivers, or reservoirs. Surface water is treated to remove sediment, microorganisms, and chemical contaminants before reaching taps.

Water Source Type
Surface Water
EPA Radon Zone

Lower potential

Zone 3
Annual Flood Risk Cost

Estimated annual flood-related costs per property

$24
Energy Burden

% of household income spent on energy — indicator of older infrastructure

2.83%

EPA Radon Zone 3 — lower radon potential, though the EPA still recommends testing all homes.

Water Quality Testing in ZIP 94933

Tap Water & Well Testing Recommendations

Residents in ZIP code 94933 served by Marin Municipal Water District can test tap water or private well systems to verify water purity. Testing detects hidden contaminants before they impact family health.

Tap Water Testing Steps

  • 1.Conduct a certified lead check if your home was constructed before 1986.
  • 2.Use certified lab testing kits rather than uncalibrated test strips for regulated compliance.
  • 3.Sample water from both your kitchen faucet and water heater to compare line purity.

Private Well Testing Steps

  • •Test for Coliform bacteria and Nitrates annually.
  • •Test for heavy metals, radon, and PFAS every 3 years.
  • •Send samples to a state-certified drinking water laboratory recognized by California State Water Resources Control Board.
Certified Lab Testing: Always use an EPA-certified drinking water laboratory in CA for formal legal or real estate compliance testing.

🛡 What Should You Do? — ZIP 94933 Recommendations

  • ⚠ Use a certified NSF/ANSI 53 filter for drinking and cooking water if you have young children
  • ⚠ Never give unfiltered tap water to infants in formula — use certified bottled or filtered water
  • ⚠ Request a copy of the Consumer Confidence Report to see what was detected and when
  • ⚠ Call the EPA Safe Drinking Water Hotline: 1-800-426-4791

Recommended Water Treatment Systems:

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NSF 53 Lead Pitcher Filter

Specifically certified to reduce lead and copper at the tap.

Lead Filter Guide →
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NSF 58 Under-Sink RO System

Advanced filtration for PFAS, fluoride, nitrates, and organic chemicals.

RO System Guide →

Frequently Asked Questions — ZIP 94933 Water Quality

Is tap water safe to drink in ZIP code 94933?+
Tap water in 94933 (Forest Knolls, CA) meets major standards but has a grade of C due to minor past violations. Vulnerable populations may want to use a certified filter as a precaution.
How do I get my water tested in ZIP 94933 (Forest Knolls, CA)?+
To test water quality in ZIP 94933, you can order a certified drinking water test kit or send water samples to an EPA/NELAP certified laboratory in CA. Certified testing checks for lead, coliform bacteria, nitrates, hardness, and PFAS that standard test strips miss. Contact California State Water Resources Control Board for a list of certified regional labs.
How hard is the tap water in 94933?+
Tap water in 94933 is classified as Hard with an estimated mineral hardness of 136 mg/L (8 GPG). An ion-exchange water softener or descaler is recommended to prolong the life of water heaters, dishwashers, and plumbing.
Should I test private well water in 94933?+
Yes. Unlike municipal systems, private wells in 94933 are not regulated by the EPA or local utilities. Private well owners should test their water annually for coliform bacteria and nitrates, and every 3 to 5 years for heavy metals (lead, arsenic) and volatile organic compounds.
What is the lead level in 94933 tap water?+
Lead level data is not available in EPA records for 94933. Contact your utility for details.
Is there an active boil water notice in 94933?+
There are currently no active boil water advisories on record for 94933. Water treatment systems are operating within normal parameters.
Who provides tap water to 94933?+
Tap water in ZIP code 94933 is provided by Marin Municipal Water District (EPA ID: CA2110002), serving approximately 186,895 residents.
What water filter should I use in 94933?+
Based on water metrics for 94933, we recommend Lead & Microplastic Filter. Look for certifications such as NSF/ANSI 53 (Lead Reduction), NSF/ANSI 42 (Particulate/Taste).

Data Sources & Methodology

Water quality data for ZIP code 94933 is compiled from the EPA Safe Drinking Water Information System (SDWIS), EPA ECHO enforcement database, UCMR5 unregulated contaminant monitoring, and Consumer Confidence Reports filed by Marin Municipal Water District. Safety scores are composite metrics derived from violation history, lead levels, enforcement actions, and infrastructure risk indicators. Data reflects a 5-year monitoring window. Last dataset update: 2024. View EPA source data →