01The verdict: is Cobb water safe?
Cobb's drinking water has significant quality concerns based on EPA testing data. With a grade of C+ (69.2/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 2 water systems serve approximately 4,208 residents using groundwater (wells).
Copper is over its legal limit
Measured at 2.90 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 ↓4K people, 2 systems
All figures on this page come from federal EPA compliance and testing data for the systems serving this city.
See the systems ↓5 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 ↓Cobb's drinking water received a grade of C+ (69.2 out of 100), indicating fair water quality. The city's 2 water systems serve approximately 4,208 residents using groundwater.
Lead levels were measured at 5.8 ppb (90th percentile), which is within EPA limits but above recommended levels. This system has not yet been tested for PFAS under the EPA UCMR 5 program. The system has 24 violations on record, including 3 health-based violations. 10 remain unresolved.
Cobb ranks #516 out of 690 cities in California for water quality, placing it below average in the state. Cobb 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. While lead levels are within EPA limits, they are above the recommended 5 ppb threshold that health organizations consider ideal. A point-of-use filter adds an extra layer of protection.
02What's in Cobb's water
Every contaminant flagged in Cobb, 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. | 5.8 | 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. | 2.90 | 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
03Cobb'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 24 violations on record, including 3 health-based violations. 10 remain unresolved.
6 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 5.2 ppb since 1995. Latest reading: 5.8 ppb (2025) — 39% of the action level. Sampled at higher-risk homes (90th percentile).
▲ Up 1.4 mg/L since 1993. The latest reading (2.9 mg/L, 2009) is over the action level. Sampled at higher-risk homes (90th percentile).
04Where Cobb's water comes from
Cobb'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.
2 systems
2 water systems, operated under local government ownership.
4,208 people
Residents served across Cobb'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 local government ownership and serves approximately 4,208 people through 2 water systems.
| System name | PWSID | Population | Source |
|---|---|---|---|
| COBB AREA COUNTY WATER DISTRICT | CA1710012 | 3,515 | Groundwater |
| LOCH LOMOND MUTUAL WATER CO | CA1700518 | 693 | Groundwater |
Water bodies near Cobb
These water bodies shape the regional watershed and can indirectly affect groundwater quality.
05Pressure on Cobb's watershed
Outside forces that shape what reaches the treatment plant. None of these is a verdict on the tap by itself — but each adds pressure worth knowing about.
Flood & storm history
8 federal disaster declarations on record for Lake County. Flooding and severe storms can overwhelm treatment plants, cause sewage overflows, and push runoff into supplies.
06How Cobb compares
Scores for nearby California cities on one line, with the average marked.
dashed line = California average (57/100)
Cobb scores 69.2/100 — above the California average of 57/100. It outscores 6 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.→
07What to do at home
Steps matched to what testing actually found in Cobb's water — not generic advice.
Filter drinking & cooking water
NSF-certified water filter. Lead detected at 5.8 ppb
Compare tested filters →Flush taps & check your service line
Lead leaches from pipes as water sits. Run cold water 30 seconds before drinking (especially mornings), and ask the utility whether your address still has a lead service line.
Lead risks explained →Watch for Cobb alerts
This area has a history of flood declarations — after severe weather, watch for boil-water advisories from the utility, and check the live alerts on this page.
All water alerts →Frequently asked questions
Is Cobb, CA tap water safe to drink?
Cobb's water quality earned a grade of C+ (69.2/100). Some concerns have been identified. Consider a water filter for an extra layer of protection. The city ranks #516 out of 690 cities tested in California.
What contaminants are in Cobb's water?
Lead was measured at 5.8 ppb (90th percentile). 24 violations are on record.
How is Cobb'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 Cobb?
While lead levels are within EPA limits, a filter adds extra protection. Based on current data, basic filtration should suffice for additional peace of mind.
Where does Cobb's water come from?
Cobb's water is sourced from Groundwater. The city has 2 water systems serving approximately 4,208 residents.
What health violations has Cobb's water system had?
Cobb has 3 health-based violations on record. The most recent violation was recorded in June 2025. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 10 violations remain unresolved.
Is Cobb's groundwater at risk of contamination?
Cobb 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 24 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 Cobb's water compare to other cities?
Cobb ranks #516 out of 690 cities in California (better than 25% of state cities) and #10799 out of 15382 cities nationally (30th percentile). The grade of C+ reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.