B
70

Good Water Quality

Big Oak Flat, CA 95305

Tuolumne County · Population served: 3,400 · Data updated March 2026

Water Systems Serving This Area

🏔
GROVELAND COMMUNITY SERV DIST
Surface water · Pop. 3,400
PWSID: CA5510009

PFAS / Forever Chemicals

2 detected 1 above EPA limits
CompoundLevelEPA MCLHealth GuidelineStatus
PFBA7.2 pptNo standard500 pptUnregulated
PFOS4.9 ppt4 ppt4 pptExceeded

Violation History (Last 5 Years)

5Total (5yr)
3Health-Based
1Major

Water Quality Summary

Understanding Your Water in Big Oak Flat

Tap water quality in Big Oak Flat, California (95305) receives an overall grade of B (Good) with a score of 70 out of 100, based on analysis of EPA compliance data, contaminant testing, and violation history. This is 11 points below the California state average of 81. The area is served by Groveland Community Serv Dist, a surface water system providing water to approximately 3,400 people. Notably, 1 PFAS compound exceeds EPA limits — a significant concern given the persistent nature of these chemicals. Over the past 5 years, water systems here have accumulated 5 violations, including 3 health-based violations.

Your Score 70/100 B
vs State 11 pts below California avg (81)
vs National 5 pts below national avg (75)

What a Grade B Means

A score of 70/100 means the water in Big Oak Flat, CA is generally good and meets EPA standards, with only minor areas of concern. There may be low levels of detectable contaminants or a small number of non-critical violations. Most residents can feel comfortable with their tap water quality, though basic filtration can provide an extra layer of protection.

Surface water: sourced from rivers, lakes, or reservoirs

Common Questions

Frequently Asked Questions

Based on EPA data, tap water in Big Oak Flat, California receives a grade of B (Good) with a score of 70/100. This indicates the water meets federal standards and has relatively few concerns. However, individual homes may still have localized issues such as lead from old plumbing.

ZIP code 95305 is served by 1 water system using surface water sources, providing water to approximately 3,400 people. Surface water systems are more susceptible to contamination from agricultural runoff, industrial discharge, and weather events, but typically undergo more extensive treatment including filtration and disinfection.

No lead data is currently available for ZIP code 95305. This may mean lead testing results haven't been reported recently, or the serving water system uses monitoring waivers. You can request a free lead test kit from most water utilities or purchase a certified home testing kit.

Yes — 2 PFAS compounds were detected in water serving Big Oak Flat, California, and 1 exceeds EPA maximum contaminant levels. PFAS are persistent chemicals linked to cancer, immune system effects, and developmental issues. A reverse osmosis or activated carbon filter certified for PFAS removal is recommended.

Water systems serving Big Oak Flat, California have received 5 violations in the last 5 years, including 3 health-based violations. Violations can range from paperwork issues (monitoring & reporting) to serious health-based violations where contaminant levels exceeded safe limits. Review the violation details above for specifics.

Based on detected contaminants (PFAS), residents in Big Oak Flat, California should consider: Reverse osmosis (RO) system — most effective for PFAS, lead, and other contaminants. Always look for filters with NSF/ANSI certification for the specific contaminants you want to remove.

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