By SCWS Team
Published February 17, 2026 · 10 min read
California has some of the highest naturally occurring uranium levels in groundwater in the United States. The Central Valley, in particular, has extensive uranium contamination affecting hundreds of public water systems and countless private wells.
While uranium sounds alarming—it's radioactive and associated with nuclear energy—the health concerns in drinking water are actually related to its chemical toxicity to the kidneys rather than radiation exposure. Understanding this distinction helps you make informed decisions about testing and treatment.
Understanding Uranium in Groundwater
Uranium is a naturally occurring radioactive element found in soil and rock throughout the world. When groundwater contacts uranium-bearing geological formations, the uranium dissolves into the water.
Where Uranium Comes From
In California, uranium contamination is primarily natural:
- Granitic rocks: Sierra Nevada foothills and other granite formations
- Marine sedimentary deposits: Ancient seabeds now underground
- Alluvial deposits: River sediments derived from uranium-bearing source rocks
- Phosphate-rich formations: Phosphate rock often contains uranium
Human activities can also contribute to uranium contamination through mining operations, phosphate fertilizer production, and nuclear facility releases, though natural sources dominate in California.
High-Risk Areas in California
Highest Uranium Concentrations
- Eastern San Joaquin Valley: Kern, Tulare, Kings, Fresno counties—some of the highest levels in the nation
- Southern San Joaquin Valley: Extensive contamination from natural sources
- Mojave Desert region: Natural occurrence from desert geology
- Sierra Nevada foothills: Granite formations contain uranium
- Parts of Riverside and San Diego counties: Variable by location
Health Effects of Uranium Exposure
Chemical Toxicity (Primary Concern)
The EPA's uranium standard is based on kidney toxicity, not radiation:
- Kidney damage: Uranium accumulates in kidney tissues, causing inflammation and impaired function
- Nephrotoxicity: Long-term exposure above the MCL can lead to chronic kidney disease
- Dose-response relationship: Higher concentrations and longer exposure increase risk
Radiation Exposure (Secondary Concern)
While uranium is radioactive, at typical groundwater concentrations the radiation dose is relatively low. The chemical toxicity threshold is reached before significant radiation damage would occur. However, drinking water with uranium does contribute to total radiation exposure from all sources.
Vulnerable Populations
- People with existing kidney disease
- Children (developing bodies more susceptible)
- Pregnant women (potential fetal effects)
- Elderly individuals with declining kidney function
Uranium Standards and Regulations
| Standard | Level | Notes |
|---|---|---|
| EPA MCL | 30 µg/L | Maximum Contaminant Level; enforceable for public systems |
| California MCL | 20 pCi/L | California also uses picocuries (radioactivity measure) |
| EPA MCLG | 0 µg/L | Health goal; no level considered completely safe |
Testing for Uranium
Uranium testing is straightforward but not included in standard water tests:
- Request specific uranium testing: Ask for "uranium" or "gross alpha with uranium"
- Certified laboratory: Use a state-certified drinking water lab
- Cost: $30-60 for uranium analysis
- Sample handling: Normal water sampling procedures; no special requirements
When to Test
- When purchasing property with a private well in California
- If you're in the Central Valley or other high-risk area
- As part of comprehensive water quality testing
- If neighbors have found elevated uranium
- Every 3-5 years in areas with known uranium presence
Treatment Options
Anion Exchange
- How it works: Specialized resins capture uranium ions from water
- Effectiveness: 90-95% uranium removal
- Best for: Whole-house treatment
- Cost: $1,500-4,000 for residential systems
- Maintenance: Resin regeneration or replacement; spent resin disposal
Reverse Osmosis
- How it works: Membrane filtration removes dissolved uranium
- Effectiveness: 90-99% uranium removal
- Best for: Point-of-use drinking water treatment
- Cost: $200-600 for under-sink systems
- Maintenance: Filter and membrane replacement
Coagulation/Filtration
- How it works: Chemical addition causes uranium to precipitate for filtration
- Effectiveness: Variable, 80-95%
- Best for: Higher contamination levels; professional systems
What Doesn't Work
- Carbon filters: Activated carbon does NOT remove uranium
- Standard water softeners: Not designed for uranium removal
- Boiling: Concentrates uranium; makes problem worse
- UV treatment: Kills bacteria; doesn't affect uranium
Frequently Asked Questions
What is the safe level of uranium in drinking water?
The EPA Maximum Contaminant Level (MCL) for uranium in drinking water is 30 micrograms per liter (µg/L or ppb). This standard is based on uranium's chemical toxicity to the kidneys, not its radioactivity. California follows the same 30 µg/L standard.
Where in California has high uranium in groundwater?
Uranium contamination is widespread in California's Central Valley, particularly in Kern, Tulare, Kings, and Fresno counties. The eastern San Joaquin Valley has some of the highest levels in the nation. Parts of the Mojave Desert and Sierra Nevada foothills also have elevated uranium.
What are the health effects of uranium in drinking water?
Uranium's primary health concern in drinking water is kidney damage (nephrotoxicity) rather than radiation exposure. Long-term exposure above the MCL can cause kidney inflammation and impaired kidney function.
How do you remove uranium from well water?
Effective uranium treatment options include anion exchange (90-95% removal), reverse osmosis (90-99% removal), and coagulation/filtration systems. Standard carbon filters do NOT remove uranium.
Concerned About Uranium in Your Well?
Southern California Well Service can help coordinate water testing and connect you with treatment solutions. We serve San Diego and Riverside Counties.
Call (760) 463-0493