California Wastewater Treatment Plants

1. Introduction

California represents the largest and most complex wastewater market in the United States. Driven by chronic water scarcity, seismic risks, and stringent environmental regulations, the state’s infrastructure is undergoing a massive paradigm shift from “waste disposal” to “resource recovery.” California operates approximately 900 active wastewater treatment facilities, managing a total design capacity exceeding 4.5 billion gallons per day (BGD).

The engineering landscape is defined by the mandates of the State Water Resources Control Board (SWRCB) and nine Regional Water Quality Control Boards. Currently, the state is investing heavily in Potable Reuse (IPR and DPR) projects, nutrient removal upgrades for the San Francisco Bay, and biosolids modernization. For consulting engineers and equipment vendors, California offers the highest density of large-scale capital improvement projects in the nation, with a clear trajectory toward closed-loop water cycles and carbon-neutral operations.

California accounts for roughly one in eight of the publicly owned treatment works tracked in our national directory of US wastewater treatment plants, and it carries a disproportionate share of the country’s largest ocean dischargers and its advanced water purification capacity. This page serves as the state-level index: it profiles the largest facilities, maps every plant covered on this site by region, summarizes the regulatory drivers that shape design here, and provides the capacity and treatment-level benchmarks engineers use when sizing or specifying equipment for a California project.

2. Recent Developments & Projects

In the last 36 months, California’s wastewater sector has pivoted aggressively toward Advanced Water Purification (AWP). The defining development is the “Pure Water” movement, with multi-billion dollar programs active in San Diego, Los Angeles, and Santa Clara counties. These projects utilize Full Advanced Treatment (FAT)—typically Microfiltration, Reverse Osmosis, and UV/Advanced Oxidation—to generate potable water supplies.

Significant funding has been mobilized through the Clean Water State Revolving Fund (CWSRF) and the federal Water Infrastructure Finance and Innovation Act (WIFIA). Notably, the EPA has issued master loans exceeding $1.5 billion to support these water resilience projects. Furthermore, the San Francisco Bay Area is grappling with the new Nutrient Watershed Permit, driving upgrades at over 30 facilities to reduce nitrogen loads, a major shift for plants that historically relied on tidal dispersion.

Three secondary trends are worth tracking alongside the headline reuse programs. First, organics diversion under SB 1383 has turned digesters into merchant assets, with several agencies now accepting hauled food waste and fats, oils, and grease under tipping-fee contracts. Second, seismic resilience has become a funding category in its own right, particularly for Bay Area plants sited on bay mud and for outfalls crossing liquefiable soils. Third, PFAS source control has moved from monitoring to pretreatment strategy, since most facilities cannot economically remove per- and polyfluoroalkyl substances from a full plant flow and instead target industrial contributors and landfill leachate at the point of discharge to the collection system.

3. Top 20 Largest Treatment Plants

The following list ranks California’s wastewater treatment plants by Design Average Dry Weather Flow (ADWF) capacity. These facilities represent the backbone of the state’s sanitary infrastructure.

*Note: Capacities listed are Average Dry Weather Flow design limits. Wet weather peak capacities are significantly higher.

Detailed Profiles of the Top 5 Largest Plants

4. California Treatment Plant Directory by Region

California’s treatment capacity is not distributed evenly. Roughly two-thirds of the state’s design flow sits in the coastal metropolitan corridors of Los Angeles, Orange County, San Diego, and the San Francisco Bay Area, where large regional authorities operate a small number of very large plants. Inland, the pattern inverts: the Central Valley and Central Coast rely on mid-size municipal facilities, many of which discharge to inland surface waters or to land and therefore carry tighter nutrient and salinity limits than their coastal counterparts. The sections below index every California facility profiled on this site, grouped by the region and the receiving-water regime that governs its design.

Los Angeles County

Los Angeles County concentrates more treatment capacity than most states. Two ocean dischargers — Hyperion and JWPCP — account for approximately 850 MGD of design flow between them, while a network of inland water reclamation plants operated by LASAN and LACSD produces tertiary effluent for groundwater recharge in the Montebello Forebay and San Fernando Valley.

Hyperion, process detail. Our profile of the Hyperion Wastewater Treatment Plant covers the liquid train in depth: bar screens and aerated grit removal, advanced primary clarification with polymer addition, and high-purity oxygen activated sludge in covered reactors that limits both footprint and odor emissions on a site hemmed in by residential neighborhoods and airport operations. The oxygen basins run at mixed liquor concentrations well above conventional air-activated sludge, which is what allows a 450 MGD plant to fit on roughly 144 acres.

Hyperion, reclamation and reuse. The Hyperion Water Reclamation Plant entry addresses the facility in its resource-recovery role — the effluent management strategy, the recycled water deliveries to the West Basin barrier system, and the biosolids program that produces Class A material for agricultural land application in Kern County.

Hyperion, technology program. A separate article on innovation at the Hyperion facility tracks Operation NEXT, the phased conversion toward 100% recycling by 2035. The engineering challenge is retrofitting membrane bioreactors and reverse osmosis into an operating 450 MGD plant without taking capacity offline, which drives a piloting and staged-cutover sequence rather than a conventional design-bid-build delivery.

Donald C. Tillman Water Reclamation Plant. The Donald C. Tillman Water Reclamation Plant in Van Nuys is LASAN’s principal San Fernando Valley facility, producing tertiary effluent at up to approximately 80 MGD. Its output supports the Japanese Garden, Lake Balboa, and Sepulveda Basin irrigation demand, and it is a central asset in the city’s plan to recharge the San Fernando Groundwater Basin with purified water.

JWPCP, county service area. A companion article covers the JWPCP within the Los Angeles County system, including how flow is routed from the upstream water reclamation plants and how the Total Energy Facility offsets plant load with digester gas cogeneration.

San Jose Creek Water Reclamation Plant. The San Jose Creek Water Reclamation Plant in Whittier is the largest of LACSD’s inland reclamation facilities at roughly 100 MGD, providing tertiary effluent to the Montebello Forebay spreading grounds for managed aquifer recharge.

San Jose Creek, district operations. A second article examines San Jose Creek water reclamation operations from the district’s perspective, including how upstream reclamation plants and the downstream JWPCP share load and how solids are returned to the joint outfall system for centralized digestion.

Whittier Narrows Water Reclamation Plant. The Whittier Narrows Water Reclamation Plant in South El Monte is a mid-size tertiary facility whose entire output is directed to groundwater recharge in the Rio Hondo and San Gabriel River spreading grounds. Its permit conditions are driven by recharge criteria under Title 22 rather than by surface water quality objectives.

Los Coyotes Water Reclamation Plant. The Los Coyotes Water Reclamation Plant in Cerritos serves the southeastern portion of the county, producing tertiary effluent for the San Gabriel River and for recycled water customers in surrounding cities.

Hollywood water pollution control plant. A profile of the Hollywood water pollution control plant also sits in this group. The facility name is shared by installations in more than one state, so its classification should be confirmed before the entry is treated as a California asset in any capacity roll-up.

Orange County and the Inland Empire

Orange County operates one of the most tightly integrated water reuse systems in the world, and the Inland Empire pairs municipal treatment with Chino Basin groundwater management. Both regions design toward recycled water quality first and discharge quality second, which reverses the usual specification priorities.

Orange County Sanitation District. The Orange County Sanitation District overview covers the agency itself — its two-plant configuration, the interplant connections that allow flow balancing, and the partnership with Orange County Water District that makes the Groundwater Replenishment System possible.

Reclamation Plant No. 1. The Reclamation Plant No. 1 article covers the Fountain Valley facility, which supplies essentially all secondary effluent feeding the GWRS advanced treatment train next door. Because the downstream microfiltration step is sensitive to secondary effluent turbidity and filament content, activated sludge control at Plant No. 1 is managed against membrane fouling criteria rather than against discharge permit limits alone.

OC San treatment operations. A further profile of the Orange County Sanitation District treatment plant addresses day-to-day operations, including trickling filter and activated sludge process selection, odor control at the Fountain Valley and Huntington Beach sites, and the district’s biosolids management contracts.

IEUA Regional Plant No. 1. The Inland Empire Utilities Agency Regional Plant No. 1 in Ontario treats roughly 44 MGD and delivers recycled water into a regional distribution system used for irrigation, industrial supply, and Chino Basin recharge.

IEUA, recycled water program. A second entry on Regional Plant 1 in Ontario focuses on the agency’s recycled water and organics programs, including regional biosolids composting and the salinity management constraints that come with recharging a groundwater basin under an adjudicated judgment.

Riverside Regional Water Quality Control Plant. The Riverside Regional Water Quality Control Plant is a tertiary facility discharging to the Santa Ana River, where downstream Orange County recharge operations make the river itself part of a regional reuse chain. Nitrogen limits here are set by the basin plan objectives for the recharge area, not by conventional secondary standards.

San Bernardino Water Reclamation Plant. The San Bernardino Water Reclamation Plant is notable for its Rapid Infiltration and Extraction approach, in which secondary effluent is polished through engineered soil basins and recovered before discharge — an approach that trades land area for reduced mechanical filtration capital cost.

San Diego County and the Border Region

San Diego County combines the state’s largest advanced primary discharger with an aggressive potable reuse program and a binational treatment facility handling transboundary flow. Every major project in the county is now framed around reducing Point Loma’s ocean discharge.

Point Loma, city operations. A companion article on the Point Loma plant covers the City of San Diego’s operating context: the Metro System that conveys flow from participating agencies, the 301(h) modified permit renewal cycle, and how upstream diversion to Pure Water reduces the mass emission rates the waiver is judged against.

North City Water Reclamation Plant. The North City Water Reclamation Plant is the linchpin of Pure Water San Diego Phase 1, supplying tertiary effluent to the adjacent advanced water purification facility. Its expansion was sized around purification demand rather than around wastewater flow projections.

North City, San Diego program view. A second profile of the North City reclamation facility examines its role in the citywide recycled water distribution network and the pump station and pipeline work required to move purified water to Miramar Reservoir.

Encina Water Pollution Control Facility. The Encina Water Pollution Control Facility in Carlsbad is a joint powers facility serving six North County member agencies at roughly 40 MGD, with an ocean outfall and a growing recycled water program run by the member agencies individually.

South Bay International Wastewater Treatment Plant. The South Bay International Wastewater Treatment Plant near San Ysidro is operated under the International Boundary and Water Commission and treats flow originating in Tijuana. Its design and funding sit under a binational framework that differs substantially from a standard NPDES-permitted municipal plant, and capacity expansion here is driven by transboundary flow events rather than by local service population.

San Francisco Bay Area

The Bay Area has the highest density of separate treatment agencies in the state, and its plants now share a single dominant regulatory driver: the San Francisco Bay Nutrient Watershed Permit. Facilities that were designed for carbonaceous removal and tidal dispersion are being evaluated for nitrogen removal retrofits, and site constraints on filled bay margin land make footprint the binding limitation at many of them.

EBMUD, agency overview. The East Bay Municipal Utility District profile covers the agency across both its water supply and wastewater roles, including the interceptor system that collects flow from Oakland, Berkeley, Alameda, Albany, Emeryville, Piedmont, and the Stege Sanitary District.

EBMUD, plant profile. A dedicated article on the wastewater treatment plant operated by East Bay Municipal Utility District details the liquid and solids trains, including high-purity oxygen secondary treatment and the digester complex that anchors the district’s resource recovery program.

EBMUD, process and performance. Our East Bay MUD wastewater treatment plant entry focuses on process performance — wet weather flow management across three wet weather facilities, effluent quality trends, and the energy balance that makes the plant a net exporter of electricity.

EBMUD, Oakland site. A further article on the EBMUD wastewater treatment plant in Oakland addresses the site itself: seismic vulnerability on bay margin fill, the deepwater outfall, and the truck receiving stations that support co-digestion of hauled organic waste.

Southeast Water Pollution Control Plant. The Southeast Water Pollution Control Plant treats the majority of San Francisco’s flow in a combined sewer system, which means the plant and its associated storage and transport boxes must handle a peak wet weather flow many times the dry weather average.

Southeast, SFPUC program view. A second entry on the San Francisco Southeast Water Pollution Control Plant covers the Sewer System Improvement Program, the Biosolids Digester Facilities Project, and the environmental justice commitments attached to a plant sited in the Bayview-Hunters Point neighborhood.

San Jose-Santa Clara Regional Wastewater Facility. The San Jose-Santa Clara Regional Wastewater Facility is the largest advanced wastewater treatment plant on San Francisco Bay, with nitrification, denitrification, and filtration in the standard train. Its discharge is limited in part to protect salt marsh habitat in the Artesian Slough, an unusual permit driver that constrains freshwater flow rather than pollutant mass alone.

San Jose/Santa Clara, plant operations. A companion profile of the San Jose/Santa Clara Water Pollution Control Plant covers unit process detail and the multi-decade capital improvement program rebuilding aging headworks, digesters, and lagoon-based solids handling.

City of San Jose facility view. The City of San Jose wastewater treatment plant article addresses the ownership and governance structure, in which San Jose operates the plant on behalf of tributary agencies under a long-standing joint use agreement.

Regional facility, Santa Clara County service area. A further entry on the regional wastewater facility serving Santa Clara County looks at recycled water production for the South Bay Water Recycling system and the advanced purification demonstration work supporting future potable reuse.

Central Contra Costa Sanitary District. The Central Contra Costa Sanitary District wastewater treatment plant serves central Contra Costa County with secondary treatment and multiple-hearth incineration for solids, an increasingly rare configuration in California as agencies migrate toward digestion and beneficial reuse.

Central Contra Costa, Martinez site. A second article covers the district’s treatment plant in Martinez, including the recycled water program supplying nearby refineries and the ongoing evaluation of solids handling alternatives.

Central Contra Costa, sustainability program. Our article on the district’s sustainable operations approach examines energy recovery, greenhouse gas reduction, and the asset management framework that governs its capital planning.

Delta Diablo. The Delta Diablo Sanitation District wastewater treatment facility in Antioch is one of California’s earliest examples of industrial recycled water at scale, supplying tertiary effluent as cooling water to nearby power generation and reducing regional freshwater demand.

Walnut Creek area treatment. The Walnut Creek sewage treatment plant entry covers treatment serving the Walnut Creek area of central Contra Costa County, where collection system flow is conveyed to regional treatment rather than handled at a standalone city plant.

Alvarado Wastewater Treatment Facility. The Alvarado Wastewater Treatment Facility in Union City is operated by Union Sanitary District and serves Fremont, Newark, and Union City at roughly 33 MGD, discharging to South San Francisco Bay through a shared outfall.

Central Valley

Central Valley plants discharge to rivers and to land rather than to the ocean, which makes nutrient limits, salinity, and groundwater protection the governing design constraints. Land availability is generally better than on the coast, so treatment trains here more often use ponds, wetlands, and infiltration in place of purely mechanical processes.

Sacramento Regional Wastewater Treatment Plant. The Sacramento Regional Wastewater Treatment Plant in Elk Grove is the largest inland facility in the state, discharging to the Sacramento River upstream of the Delta. The completed EchoWater upgrade added biological nutrient removal and filtration, transforming a secondary plant into a tertiary one at a cost of roughly $1.7 billion.

Regional San, facility view. A second entry on the Sacramento Regional Wastewater Treatment Facility covers the EchoWater project itself — the biological nutrient removal basins, granular media filtration, and the sequencing required to build a major upgrade while maintaining permit compliance on an operating plant.

Fresno-Clovis Regional Water Reclamation Facility. The Fresno-Clovis Regional Water Reclamation Facility treats up to approximately 80 MGD and relies on percolation ponds for effluent disposal, making it one of the largest land-application systems in the country and a direct contributor to local groundwater recharge.

Stockton Regional Wastewater Control Facility. The Stockton Regional Wastewater Control Facility combines mechanical treatment with oxidation ponds and constructed wetlands before discharge to the San Joaquin River, a hybrid approach that provides polishing capacity and habitat value at lower operating cost than an equivalent mechanical train.

Central Coast and Ventura County

Coastal agencies outside the major metros serve smaller populations but face some of the state’s most demanding constraints: sensitive receiving waters, agricultural reuse demand, and severe limits on available land.

Monterey Regional Water Pollution Control Agency. The Monterey Regional Water Pollution Control Agency wastewater treatment facility supports both the Castroville Seawater Intrusion Project, which delivers tertiary recycled water to Salinas Valley growers, and the Pure Water Monterey advanced purification program for groundwater replenishment. It is the clearest California example of agricultural reuse and potable reuse operating from the same source flow.

Santa Cruz Wastewater Treatment Facility. The Santa Cruz Wastewater Treatment Facility serves the city and neighboring service areas with secondary treatment and ocean discharge, on a compact site where wet weather flow from an aging collection system is the dominant operating challenge.

Hill Canyon Wastewater Treatment Plant. The Hill Canyon Wastewater Treatment Plant in Thousand Oaks produces tertiary effluent discharged to the Arroyo Conejo and has pursued an energy-neutral operating strategy built on digester gas cogeneration and on-site solar generation.

5. Plants with Approved Budgets & Expansion Projects

California currently leads the nation in capital expenditure for wastewater infrastructure. Below is a detailed breakdown of active major projects.

A. Major Projects Under Construction (2024-2026)

B. Projects in Design/Planning Phase (2025-2027)

C. Recently Completed Major Projects (2022-2024)

• EchoWater Project (Sacramento Regional San): Completed in 2023. A $1.7 billion massive upgrade to tertiary treatment for biological nutrient removal (BNR) to protect the Delta.
• GWRS Final Expansion (Orange County): Completed in 2023. Increased capacity from 100 MGD to 130 MGD, recycling 100% of OC San’s reclaimable wastewater flows.

6. Regulatory & Compliance Landscape

California operates under the Porter-Cologne Water Quality Control Act, which often sets standards stricter than the federal Clean Water Act.

Key Regulations for Engineers:

• Title 22 (California Code of Regulations): The gold standard for water recycling criteria. Recent amendments now include frameworks for Direct Potable Reuse (DPR), adopted by the SWRCB in late 2023, allowing treated wastewater to be introduced directly into potable water distribution systems without an environmental buffer.
• San Francisco Bay Nutrient Watershed Permit: Requires 30+ dischargers in the Bay Area to reduce nutrient loads (Nitrogen/Phosphorus) significantly by 2029 to prevent algal blooms.
• PFAS/PFOA Monitoring: The SWRCB has issued investigative orders requiring testing for PFAS at wastewater facilities. Future NPDES permits are expected to include effluent limits for these “forever chemicals.”
• Biosolids (SB 1383): This legislation targets methane reduction and mandates the diversion of organic waste from landfills, pushing WWTPs to accept food waste for co-digestion.

How Regional Board Jurisdiction Changes the Design Basis

California’s nine Regional Water Quality Control Boards write their own basin plans, and the same treatment train can face materially different limits depending on which board issues the permit. A coastal plant in Region 4 (Los Angeles) discharging through a deep ocean outfall may operate under a 301(h) modified permit with mass emission rate limits, while a Region 5 (Central Valley) plant discharging to a river faces ammonia, nitrate, and often salinity limits that force full nitrification-denitrification and, increasingly, reverse osmosis on a side stream. Region 2 (San Francisco Bay) plants are now working under a watershed-wide nutrient permit that allocates load across dischargers rather than setting a uniform concentration limit for each.

The practical consequence for design teams is that regional board jurisdiction should be established before any process selection work begins. Two plants of identical size and influent character, one in Carlsbad and one in Modesto, will not converge on the same treatment train, and benchmarking capital cost per MGD across regions without normalizing for permit basis produces misleading numbers.

7. Technology Trends in California

Due to the high cost of water and energy, California facilities are early adopters of advanced technologies:

• Membrane Bioreactors (MBR): Becoming the standard for new reuse facilities due to high effluent quality and smaller footprints (e.g., Hyperion retrofit plans).
• UV/Advanced Oxidation (AOP): Essential for destruction of micro-constituents and pathogens in potable reuse trains.
• Thermal Hydrolysis (THP): Being deployed at SFPUC and planned for other major metros to maximize biogas production and reduce Class A biosolids volume.
• Ceramic Membranes: Gaining traction in pilot projects for their durability in tough water matrices.
• Ozone and Biologically Active Carbon (O3/BAC): Increasingly specified ahead of membranes in potable reuse trains to reduce fouling and organics load, and used as an alternative to full membrane treatment where brine disposal is impractical inland.
• Brine management: The binding constraint on inland reuse. Deep well injection, brine lines to the coast, and evaporation ponds each carry different permitting timelines, and brine disposal cost frequently exceeds the cost of the purification train it supports.

8. Comparing California Facility Classes

California facilities cluster into recognizable classes defined by receiving water, treatment level, and reuse role. The table below summarizes how those classes differ in the terms that matter for equipment selection and capital planning.

9. Benchmarking and Site Selection

Engineers, equipment suppliers, and analysts use a state directory in three distinct ways: to size an opportunity, to find a comparable facility for a design or bid basis, and to understand what a permit will require before the treatment train is fixed. Each use calls for a different reading of the same data.

Selecting a comparable facility

Match on receiving water and permit basis first, then on capacity. A 40 MGD Bay Area plant under the nutrient watershed permit is a poor analog for a 40 MGD ocean discharger even though the flows are identical, because the secondary and tertiary process trains diverge entirely. Once the permit basis matches, narrow by influent character: plants with heavy industrial contribution, high inflow and infiltration, or significant hauled waste receiving will show operating costs well outside the range predicted by flow alone.

Worked example: sizing a comparison set

Suppose a design team needs a cost and staffing benchmark for a proposed 35 MGD tertiary plant discharging to an inland river in the Central Valley. Filtering the directory by receiving water eliminates every coastal facility, which removes most of the largest plants in the state. Filtering by treatment level to tertiary with nutrient removal leaves the Sacramento and Stockton facilities as the closest regional analogs, plus Fresno-Clovis if land-based disposal is under consideration. Normalizing those plants to a per-MGD basis is only valid after adjusting for the fact that Sacramento’s tertiary capacity was added as a retrofit rather than built new, which typically carries a 25 to 40 percent premium over greenfield construction of equivalent capacity. The usable benchmark set is therefore two facilities, not twenty, and the design team should expect to supplement it with out-of-state comparables.

Comparing California to other state markets

California’s reuse-first design philosophy is not universal, and looking at neighboring state directories is often the fastest way to isolate what is genuinely a California constraint and what is simply a regional preference. The directory of Texas wastewater treatment plants covers the closest comparison by market scale, with a similar volume of large municipal facilities but a very different regulatory framework and a much larger share of direct potable reuse precedent. The Arizona wastewater treatment plants directory covers a Colorado River basin market where recharge and recovery permitting dominates plant design, and the Nevada wastewater treatment plants directory covers a return-flow credit system in which treated effluent quality is tied directly to a utility’s water supply entitlement — an arrangement with no California equivalent.

10. Directory of Facilities by Size Class

Browse our organized directory of water and wastewater treatment plants in California:

Major Regional Facilities (>100 MGD)

• Hyperion Water Reclamation Plant (Los Angeles)
• Joint Water Pollution Control Plant (Carson)
• Point Loma Wastewater Treatment Plant (San Diego)
• Sacramento Regional Wastewater Treatment Plant (Elk Grove)
• EBMUD Main Wastewater Treatment Plant (Oakland)
• OC San Plant No. 1 & No. 2 (Orange County)

Large Municipal Plants (50-100 MGD)

• Southeast Treatment Plant (San Francisco)
• Tillman Water Reclamation Plant (Van Nuys)
• San Jose Creek Water Reclamation Plant (Whittier)
• Fresno-Clovis Regional WRF (Fresno)

Mid-Size Municipal Plants (10-50 MGD)

• Inland Empire Regional Water Recycling Plant No. 1 (Ontario)
• Encina Water Pollution Control Facility (Carlsbad)
• Alvarado Wastewater Treatment Facility (Union City)
• North City Water Reclamation Plant (San Diego)
• Delta Diablo (Antioch)
• Monterey Regional Water Pollution Control Agency (Marina)
• Santa Cruz Wastewater Treatment Facility (Santa Cruz)
• Hill Canyon Wastewater Treatment Plant (Thousand Oaks)
• South Bay International Wastewater Treatment Plant (San Ysidro)

(Full directory available in our searchable database)

11. Field Notes

Working with California agencies

Procurement in California skews toward alternative delivery on large projects. Progressive design-build and construction manager at risk are now common on programs above roughly $100 million, which changes when equipment suppliers need to engage: technology selection often happens during a validation phase with the design-builder, well before a conventional bid package would exist. Suppliers who wait for a public bid advertisement on these programs are typically too late to influence the basis of design.

Wet weather is the hidden sizing driver

California’s dry weather flow figures understate the hydraulic duty at most coastal plants. Hyperion’s peak wet weather capacity is roughly 1.9 times its average design flow, and San Francisco’s combined system produces even wider ratios. Headworks, primary clarifiers, disinfection contact time, and outfall hydraulics are all sized on the peak condition, so specifying equipment against the advertised MGD figure alone will undersize the package.

12. Permitting & Design Standards Reference

California layers state requirements on top of the federal framework, and the applicable documents differ depending on whether a project produces recycled water, discharges to surface water, or manages biosolids.

Water recycling criteria in California are set by Title 22, Division 4, Chapter 3 of the California Code of Regulations, administered by the State Water Resources Control Board Division of Drinking Water. Surface water discharges are permitted under the NPDES program as delegated to the nine Regional Water Quality Control Boards under the Porter-Cologne Water Quality Control Act. Ocean discharges are additionally governed by the California Ocean Plan.

Specification checklist for a California project

1. Identify the Regional Water Quality Control Board with jurisdiction and obtain the current basin plan objectives for the receiving water.
2. Confirm whether the effluent will be recycled; if so, establish the Title 22 use category, since disinfected tertiary, disinfected secondary-23, and undisinfected requirements differ substantially.
3. Establish the design average dry weather flow and the peak wet weather flow separately, and confirm which controls each unit process.
4. Verify nutrient limits and whether the plant sits under a watershed-wide allocation rather than a fixed concentration limit.
5. Check salinity and total dissolved solids objectives for inland discharges and for any groundwater recharge component.
6. Determine the brine disposal pathway before selecting a membrane process for any inland site.
7. Confirm seismic design category and, for bay margin or liquefiable sites, whether geotechnical mitigation is included in the project scope.
8. Establish biosolids end use and whether SB 1383 organics receiving is contemplated, since co-digestion changes digester sizing, gas handling, and odor control.
9. Review energy requirements against the agency’s decarbonization commitments; several large agencies now evaluate bids on lifecycle greenhouse gas impact.
10. Confirm operator certification grade required for the facility class, as SWRCB grade requirements affect staffing cost assumptions.
11. Identify applicable AWWA, WEF, and ANSI/ASME standards for the specific equipment package.
12. Verify whether the project uses state or federal funding, since SRF and WIFIA participation trigger procurement, labor, and reporting requirements.
13. Confirm odor control performance criteria, which in dense urban settings are often set by settlement agreements rather than by regulation.
14. Document the peak-to-average ratio assumed for hydraulic structures, and have the agency confirm it in writing before final sizing.

13. Resources for Engineers & Operators

• CWEA (California Water Environment Association): The primary body for operator certification and technical conferences. Visit CWEA.
• SWRCB Division of Financial Assistance: Managing agency for SRF loans and grants.
• CASA (California Association of Sanitation Agencies): Represents legislative interests of wastewater agencies.
• SWRCB Division of Drinking Water: Administers Title 22 recycled water criteria and the direct potable reuse regulations.
• Regional Water Quality Control Boards: Nine boards issue NPDES permits and maintain the basin plans that set receiving water objectives.
• California Water Boards GeoTracker and CIWQS: Public databases for facility permits, violations, and monitoring reports.
• WateReuse California: Trade association focused on recycled water policy, research, and project development.

14. FAQ

15. Conclusion

California’s wastewater sector is the most capital-intensive and the most technically demanding in the country, and it is moving faster than any other state market toward closed-loop water systems. The direction of travel is unambiguous: ocean discharge volume is being converted into purified supply, digesters are becoming regional organics processing assets, and nutrient limits are reaching plants that spent decades operating without them. For engineers, operators, and suppliers, the practical implication is that a California facility’s advertised treatment level increasingly understates what the plant is actually being asked to deliver.

Use this directory as an index rather than a ranking. Start from the receiving water and the permitting board, narrow to the treatment class, and only then compare capacity and cost. The regional listings above link to detailed profiles of every California facility covered on this site, and the state-level comparisons in Section 9 provide the cross-market context needed to judge whether a given design constraint is genuinely a California requirement or simply local practice.