01The verdict: is Yosemite Np water safe?
Yosemite Np's drinking water has significant quality concerns based on EPA testing data. With a grade of B- (71.2/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 4 water systems serve approximately 1,836 residents using groundwater (wells).
Copper is over its legal limit
Measured at 1.40 mg/L against the EPA Action Level of 1.3 mg/L. The ledger below shows how far over — and which filter removes it.
See the measurement ↓Lead is well under the limit
90th-percentile lead is 0.0 ppb — beneath the 15 ppb federal action level and under the 5 ppb watch threshold.
See the trend ↓4 violations in the last five years
Recent compliance history is the best predictor of future problems — the year-by-year record is below.
See the record ↓Yosemite Np's drinking water received a grade of B- (71.2 out of 100), indicating fair water quality. The city's 4 water systems serve approximately 1,836 residents using groundwater.
Lead levels were measured at 0.0 ppb (90th percentile), well within EPA limits. This system has not yet been tested for PFAS under the EPA UCMR 5 program. The system has 33 violations on record, including 10 health-based violations. 22 remain unresolved.
Yosemite Np ranks #498 out of 690 cities in California for water quality, placing it below average in the state. Yosemite Np relies on groundwater, which is generally less vulnerable to surface contamination but can be affected by naturally occurring minerals like arsenic and nitrate, as well as agricultural and industrial runoff. As a small community water system, Yosemite Np may have fewer resources for advanced treatment technologies and infrastructure upgrades compared to larger utilities.
02What's in Yosemite Np's water
Every contaminant flagged in Yosemite Np, on one shared scale: distance to its own legal limit. The red line is the limit — anything past it is out of compliance, and the closer a bar gets, the less headroom the system has.
Over Limit — EPA Action Level: 1.3 mg/L
Exceeds the EPA action level. Copper leaches from household plumbing — flush taps for 30 seconds before drinking, and consider a certified filter.Full contaminants report
| Contaminant | Detected Level | EPA Limit | Unit | Category | Status |
|---|---|---|---|---|---|
| Lead (90th percentile) LeadHeavy Metal A toxic heavy metal that can leach into drinking water from older pipes, solder, and fixtures. No amount of lead in water is considered safe. Health EffectsBrain and nervous system damage in children, kidney damage, high blood pressure, and reproductive problems in adults. EPA Limit15 ppb action level Common SourcesCorrosion of lead pipes, lead solder, brass faucets, and household plumbing. | 0.0 | 15 | ppb | Inorganic | Safe |
| Copper (90th percentile) CopperInorganic A metal that enters drinking water mainly through corrosion of copper plumbing. Small amounts are essential for health, but excess levels are harmful. Health EffectsGastrointestinal distress (nausea, vomiting, diarrhea) at short-term high levels; liver and kidney damage from long-term exposure. EPA Limit1.3 mg/L action level Common SourcesCorrosion of copper household plumbing, erosion of natural deposits. | 1.40 | 1.3 | mg/L | Inorganic | Over Limit |
Cities ranked by 90th-percentile lead PF PFAS in California
Cities ranked by compounds detected Cu Copper in California
Cities ranked by 90th-percentile copper
03Yosemite Np's ten-year track record
Each box is one year. A green check means no EPA violations; a numbered badge counts that year's violations — red if any were health-based, amber if they were monitoring or paperwork issues. The system has 33 violations on record, including 10 health-based violations. 22 remain unresolved.
9 of the last ten years were clean. The numbered years had EPA violations — red when any were health-based, amber when they were paperwork or missed-testing issues.
▼ Down 10 ppb since 1993. Latest reading: 0 ppb (2027) — 0% of the action level. Sampled at higher-risk homes (90th percentile).
▼ Down 1.9 mg/L since 1993. The latest reading (1.4 mg/L, 2009) is over the action level. Sampled at higher-risk homes (90th percentile).
04Where Yosemite Np's water comes from
Yosemite Np's drinking water is drawn from underground aquifers through wells.
Groundwater
Underground aquifers reached by wells — naturally filtered, but can carry minerals like arsenic and nitrate.
Local treatment
Groundwater generally needs less treatment — typically disinfection and, where needed, mineral removal.
4 systems
4 water systems, operated under federal ownership.
1,836 people
Residents served across Yosemite Np's service area.
Groundwater is naturally filtered through rock and soil layers, generally requiring less treatment than surface water. However, it can contain naturally occurring contaminants like arsenic, radon, and minerals. Agricultural activity, septic systems, and industrial operations near well fields can introduce nitrates, pesticides, and volatile organic compounds. The system is operated by federal ownership and serves approximately 1,836 people through 4 water systems.
| System name | PWSID | Population | Source |
|---|---|---|---|
| YOSEMITE NPS-YOSEMITE VALLEY | CA2210503 | 1,000 | Groundwater |
| YOSEMITE NPS-EL PORTAL | CA2210515 | 635 | Groundwater |
| YOSEMITE NPS-WAWONA | CA2210510 | 150 | Surface Water |
| YOSEMITE NPS-HODGDON MEADOW | CA5510503 | 51 | Groundwater |
05How Yosemite Np compares
Scores for nearby California cities on one line, with the average marked.
dashed line = California average (57/100)
Yosemite Np scores 71.2/100 — above the California average of 57/100. It outscores 7 of 10 nearby cities. Full California rankings →
42.8 / 100FSan Jose, CA
28 / 100BOakland, CA
77.9 / 100FSan Diego, CA
39.7 / 100FSacramento, CA
31.2 / 100ABurlingame, CA
89.2 / 100
Compare all cities in the county — grades, violations, and contaminant data side by side.→
06What to do at home
Steps matched to what testing actually found in Yosemite Np's water — not generic advice.
Filter drinking & cooking water
NSF-certified water filter. Copper exceeds the EPA action level of 1.3 mg/L
Compare tested filters →Read your utility's annual report
Every utility must publish a yearly Consumer Confidence Report with its own testing results. It pairs well with the independent data on this page.
How to read a CCR →Watch for Yosemite Np alerts
We refresh EPA data monthly and surface new violations, advisories, and boil-water notices for your county on this page.
All water alerts →Frequently asked questions
Is Yosemite Np, CA tap water safe to drink?
Yosemite Np's water quality earned a grade of B- (71.2/100). Some concerns have been identified. Consider a water filter for an extra layer of protection. The city ranks #498 out of 690 cities tested in California.
What contaminants are in Yosemite Np's water?
Lead was measured at 0.0 ppb (90th percentile). 33 violations are on record.
How is Yosemite Np's water quality grade calculated?
The grade is based on four factors: violation history (40%), lead and copper levels (25%), PFAS contamination (25%), and regulatory compliance (10%). The score is also adjusted based on how complete the available data is. See our methodology page for full details.
Do I need a water filter in Yosemite Np?
Based on current data, basic filtration should suffice for additional peace of mind.
Where does Yosemite Np's water come from?
Yosemite Np's water is sourced from Groundwater. The city has 4 water systems serving approximately 1,836 residents.
What health violations has Yosemite Np's water system had?
Yosemite Np has 10 health-based violations on record. The most recent violation was recorded in October 2025. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 22 violations remain unresolved.
Is Yosemite Np's groundwater at risk of contamination?
Yosemite Np uses groundwater, which can be affected by naturally occurring contaminants like arsenic, radon, and nitrate, as well as agricultural runoff and industrial activity. The system has 33 violations on record that may relate to groundwater quality. Groundwater systems are generally less susceptible to surface contamination but should be monitored for emerging contaminants like PFAS.
How does Yosemite Np's water compare to other cities?
Yosemite Np ranks #498 out of 690 cities in California (better than 28% of state cities) and #10452 out of 15382 cities nationally (32th percentile). The grade of B- reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.