Stockton – California
The City of Stockton Municipal Utilities Department (MUD) manages a complex water system serving approximately 320,000 residents across Stockton and portions of San Joaquin County. Established in 1954, this comprehensive utility operates a hybrid water system that includes over 600 miles of water mains, multiple storage facilities, and treatment plants delivering roughly 25 million gallons of water daily throughout the service area.
Stockton draws its drinking water from three distinct sources: the Delta Water Supply Project (DWSP), which taps into the San Joaquin River; purchased treated water from the Stockton East Water District sourced from the Stanislaus River watershed; and approximately 20 groundwater wells throughout the city that draw from the Eastern San Joaquin Groundwater Basin. Stockton’s water system faces unique challenges including Delta water quality variations, groundwater contamination concerns in certain areas, and the need to balance multiple water sources. The city has implemented significant investments in the Delta Water Treatment Plant completed in 2012, groundwater management programs, and distribution system improvements to maintain water quality and supply reliability in this critical Central Valley hub.
Stockton Water Quality: Current Status (2024-2025)
Latest Testing Results
- Lead Levels: The most recent testing period (January-December 2023) showed 90th percentile lead levels of 5.2 parts per billion (ppb), well below the EPA action level of 15 ppb, reflecting the city’s effective corrosion control treatment and ongoing lead service line identification program.
- Testing Scope: Stockton conducts over 45,000 water quality tests annually across all service zones, with enhanced monitoring for specific contaminants of concern in the Delta and groundwater sources.
- Compliance Status: Stockton’s water meets all federal and state drinking water standards, maintaining compliance with EPA and California State Water Resources Control Board Division of Drinking Water regulations.
Diverse Water Sources
- Delta Water Supply Project: Primary surface water source (70% of supply) drawing from the San Joaquin River, treated at the city’s state-of-the-art Delta Water Treatment Plant.
- Purchased Surface Water: Secondary source (20% of supply) from the Stockton East Water District, originating in the Stanislaus River watershed via the New Melones Reservoir.
- Groundwater Wells: Tertiary source (10% of supply) from approximately 20 municipal wells throughout the city, primarily used during peak demand periods or as backup supply.
Advanced Treatment Technology
- Delta Water Treatment Plant: Modern facility using coagulation, flocculation, sedimentation, filtration, and disinfection processes specifically designed to address Delta water quality challenges.
- Disinfection Process: Multi-barrier approach using chlorine dioxide pre-treatment followed by chloramination to effectively control pathogens while minimizing disinfection byproducts.
- Corrosion Control: Optimized pH adjustment and phosphate-based corrosion inhibitors to prevent lead and copper leaching from plumbing materials, with ongoing optimization based on water quality parameters.
Infrastructure Investment
- System Improvements: Implementation of a $220 million Capital Improvement Program through 2028, focusing on water main replacements, storage facility upgrades, and treatment enhancements.
- Lead Service Line Inventory: Comprehensive mapping program to identify and replace remaining lead service lines and galvanized pipes that may contain lead, with priority given to disadvantaged neighborhoods.
- Monitoring Technology: Advanced water quality sensors throughout the distribution system providing real-time data on water quality parameters, pressure, and contaminant detection.
Customer Support and Regional Collaboration
Stockton provides extensive customer assistance including water conservation rebates, leak detection services, and payment plans for low-income residents. The city’s Water Conservation Office offers education on efficient water use practices critical in California’s drought-prone climate. Stockton participates in the Eastern San Joaquin Groundwater Authority to implement the Sustainable Groundwater Management Act (SGMA) and address historical overdraft of the basin. The city’s commitment to environmental justice includes targeted outreach to disadvantaged communities and multilingual communication about water quality and system improvements. Stockton’s forward-looking approach balances reliable water delivery with conservation, groundwater protection, and Delta ecosystem considerations in this important agricultural and urban region.
Recommendations for Stockton Residents
Request Water Testing
Contact Stockton Municipal Utilities Department at (209) 937-8700 or visit stocktonca.gov/water to request water quality testing, especially if your home was built before 1986 or if you notice changes in water taste, odor, or appearance.
Conserve Water
Apply for rebates on high-efficiency fixtures, smart irrigation controllers, and turf replacement through the Water Conservation Office. Call (209) 937-5001 or visit stocktonca.gov/savewater to learn about water regulations and available programs.
Consider Filtration
For homes receiving groundwater or in older neighborhoods, consider using NSF-certified filters (Standard 53 for lead, Standard 42 for taste/odor). Filter pitchers are cost-effective options for improved taste, especially during seasonal Delta water quality changes.
Run Your Tap
If water has been sitting in pipes for 6+ hours, run cold water for 1-2 minutes before using for drinking or cooking. Always use cold water for consumption, as hot water can contain higher levels of metals from your household plumbing system.
Report Water Issues
Contact Stockton Municipal Utilities Department immediately at (209) 937-8341 for water main breaks, pressure problems, or quality concerns. For after-hours emergencies, call the 24-hour emergency line at (209) 937-8341. Use the Ask Stockton app to report non-emergency issues.
Frequently Asked Questions
Is Stockton’s tap water safe to drink?
Yes, Stockton’s tap water consistently meets all federal and state drinking water standards. The city’s Delta Water Treatment Plant uses advanced technology to ensure water quality, and the blended system of surface and groundwater sources undergoes comprehensive treatment and monitoring.
Recent testing shows lead levels well below EPA action limits, with 90th percentile results at 5.2 ppb. While Stockton has relatively few lead service lines compared to older eastern cities, homes built before 1986 may have copper pipes with lead solder. The utility’s corrosion control program effectively manages this risk, but free testing is available for concerned residents, especially those in older neighborhoods.
Residents may notice seasonal taste and odor variations, particularly when Delta water conditions change, but these aesthetic issues do not indicate health concerns.
Why does my water sometimes taste or smell different?
Seasonal variations in taste and odor are normal in Stockton due to several factors:
• Source water changes: The proportion of Delta water, purchased surface water, and groundwater in your supply can vary seasonally
• Delta conditions: Algae blooms in the Delta during warmer months can cause earthy or musty tastes that are removed during treatment but may occasionally be noticeable
• Chloramine disinfection: The chloramine used to keep water safe throughout the distribution system can be more noticeable to some sensitive individuals
• Groundwater minerals: When groundwater use increases during peak demand periods, you may notice increased hardness
These aesthetic variations do not indicate health concerns. Simple solutions include refrigerating water before drinking, using a carbon filter pitcher, or adding a slice of lemon. If you notice sudden or extreme changes in taste, odor, or appearance, please report them to the Utilities Department at (209) 937-8700.
What is the Delta Water Supply Project?
The Delta Water Supply Project (DWSP) is Stockton’s landmark water infrastructure investment that fundamentally transformed the city’s water system:
• Purpose: Developed to reduce groundwater overdraft, increase drinking water quality, and provide a reliable surface water supply
• Completion: The $220 million project was completed in 2012 after nearly a decade of planning and construction
• Components: Includes an intake on the San Joaquin River, a 30 million gallon per day treatment plant (expandable to 60 MGD), and transmission pipelines
• Water Rights: Secured through a long-term water right permit allowing Stockton to divert up to 33,600 acre-feet annually from the Delta
• Treatment Process: Utilizes advanced technologies including pre-oxidation, membrane filtration, and multi-stage disinfection specifically designed to address Delta water quality challenges
The DWSP now provides approximately 70% of Stockton’s water supply, reducing dependence on purchased water and allowing groundwater levels to recover. This landmark project exemplifies Stockton’s commitment to sustainable water management and infrastructure investment.
How does Stockton address water conservation?
Stockton implements a comprehensive water conservation approach due to California’s drought vulnerability:
Year-Round Water Rules:
• Even-numbered addresses water on Tuesday, Thursday, and Saturday
• Odd-numbered addresses water on Wednesday, Friday, and Sunday
• No watering between 11 a.m. and 6 p.m. any day
• No watering within 48 hours after measurable rainfall
Conservation Programs:
• Rebates for high-efficiency toilets, washing machines, and smart irrigation controllers
• Cash-for-grass program offering rebates for turf removal
• Free water-wise house calls to help identify leaks and improve efficiency
• Water-wise landscaping workshops and demonstration gardens
During severe drought, additional restrictions may be implemented based on state mandates and local water supply conditions. Current water conservation stage and information are available at stocktonca.gov/savewater or by calling (209) 937-5001.
Water Quality Considerations
Disinfection Byproducts
Source: Form when chlorine-based disinfectants react with naturally occurring organic matter in Delta water and other surface water sources
Health Concerns: Potential increased risk of bladder cancer and reproductive effects with long-term exposure to elevated levels
Current Status: Levels consistently below EPA regulatory limits due to optimized treatment processes at the Delta Water Treatment Plant including enhanced coagulation and chlorine dioxide pre-oxidation
Seasonal Variation: Higher during summer months when warmer temperatures and increased organic matter in Delta water create conditions more favorable for byproduct formation
Nitrates in Groundwater
Source: Agricultural fertilizers, animal waste, and septic systems that have infiltrated portions of the Eastern San Joaquin Groundwater Basin over decades of agricultural and urban development
Health Concerns: High nitrate levels can reduce oxygen transport in the bloodstream, particularly dangerous for infants and pregnant women
Management Approach: Stockton monitors nitrate levels in all groundwater wells and has taken several offline or installed treatment where elevated levels were detected; surface water blending further reduces concentrations
Current Status: All water delivered to customers meets EPA and California standards for nitrates; ongoing groundwater monitoring and management through the Sustainable Groundwater Management Act implementation
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