California Groundwater Guide: Aquifers, Wells & Water Quality

California’s Groundwater System

Groundwater is a vital resource in California, serving both residential and agricultural needs. Understanding the state’s hydrogeological systems is essential for property owners relying on private wells.

The Central Valley Aquifer System is one of North America’s most productive and heavily used aquifers, supplying water to millions of residents and agriculture. Additional major aquifers include the Los Angeles and San Francisco Bay basin formations, with fractured-rock aquifers in mountain regions.

The major aquifer systems in California include:

• Central Valley Aquifer System (largest)
• Los Angeles Basin aquifers
• San Francisco Bay Basin aquifers
• Sierra Nevada fractured-rock aquifers

Each of these systems has different depths, yields, and water quality characteristics that affect well drilling costs and water treatment needs.

Well Water in California

40% of California’s population relies on groundwater, with 80% of groundwater supporting agricultural irrigation in the Central Valley. This reliance on private wells is particularly important in rural communities where municipal water systems may not be available.

The average well depth in California ranges from 150-500 feet, depending on the aquifer system accessed and local geology. Well drilling costs typically range from $18-$32 per foot, though this varies based on:

• Aquifer depth and geology in your specific location
• Soil and rock composition requiring different drilling techniques
• Well diameter and final depth required
• Local California regulations and permit requirements
• Contractor experience and equipment availability

Common Water Quality Issues in California

California residents may encounter various groundwater quality challenges depending on geology and location:

• Arsenic contamination in Central Valley wells
• Nitrate pollution from agricultural fertilizers
• Selenium in some San Joaquin Valley wells
• Per- and polyfluoroalkyl substances (PFAS) in coastal areas

Regular water testing is essential for California well owners. The state recommends testing at least annually for coliform bacteria and every three to five years for a comprehensive analysis including minerals, contaminants, and chemical parameters.

California Well Regulations

All new wells in California must comply with state regulations. California Department of Water Resources and regional water boards regulate groundwater. Well drilling requires contractor licenses and groundwater sustainability plans mandatory under SGMA. ensures that:

• New wells meet minimum construction standards
• Proper well spacing protects other water users
• Contamination risks are minimized
• Well drillers possess appropriate training and licenses

Homeowners should always hire licensed well contractors to ensure compliance with these regulations.

Drought & Climate Impacts on California Groundwater

California’s severe drought has caused significant groundwater depletion, particularly in the Central Valley where land subsidence exceeds 28 feet in some areas. Climate change threatens water availability and recharge patterns. Groundwater conservation and sustainable management are increasingly important for long-term water security in California.

Finding a Groundwater Contractor in California

Groundwater World connects property owners with licensed well contractors throughout California. Whether you need:

• New well drilling for a new property
• Well rehabilitation or repair services
• Water quality testing and analysis
• Pump installation and maintenance
• Water treatment system design and installation

Our directory features qualified contractors experienced in California’s unique geological conditions. Browse our complete directory of California groundwater professionals to find the right contractor for your needs.