California's water treatment industry focuses on engineering, technology, and effective management of water resources. Companies develop solutions that address contamination, compliance, and resource recovery. Providers range from large firms, such as engineering consultants, to specialized manufacturers of filtration and purification systems. The industry is experiencing shifts toward sustainability, with innovations in membrane technology and alternative water sources gaining traction. Municipalities and private sectors are increasingly adopting advanced treatment methods to ensure safe drinking water and environmentally sound practices, reflecting a robust commitment to improving water quality amid climate change challenges.

This list includes 21 companies thriving in California's water treatment sector, with a mix of sizes, founding years, and specialties. From large firms like Brown and Caldwell, which employs thousands, to smaller entities like Trussell, each company plays a vital role in addressing crucial water management needs. Founded between 1904 to 2016, these businesses demonstrate local resiliency and a forward-thinking approach in areas such as wastewater reclamation, water purification, and compliance consulting, ensuring regulatory mandates are met while enhancing operational efficiencies for their diverse client bases.

Read on to explore the top water treatment companies in California.

Top 21 Water Treatment Companies in California

1. Brown and Caldwell

• Website: brownandcaldwell.com
• Ownership type: Private
• Headquarters: Walnut Creek, California, United States (USA)
• Employee distribution: United States (USA) 98%, Other 2%
• Latest funding: Other (Grant), $650,000, January 2025
• Founded year: 1947
• Headcount: 1001-5000
• LinkedIn: brown-and-caldwell

Brown and Caldwell is an environmental consulting and engineering firm based in Walnut Creek, California, founded in 1947. With a workforce of approximately 2,475 employees, the company specializes in water management and infrastructure solutions. Their service offerings include climate change resilience, compliance and permitting, wastewater reclamation, and water supply and treatment. Brown and Caldwell is known for its innovative approaches to environmental challenges, such as their work on potable reuse without reverse osmosis, which aims to provide cost-effective and sustainable water solutions. The firm actively engages with municipalities and private sector clients, demonstrating its relevance and commitment to improving water resources and management practices. Recently, they received a grant of $650,000 in January 2025, further supporting their initiatives in the water treatment field.

2. Kennedy Jenks

• Website: kennedyjenks.com
• Ownership type: Corporate
• Headquarters: San Francisco, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Latest funding: December 2014
• Founded year: 1919
• Headcount: 201-500
• LinkedIn: kennedyjenks-consultants

Kennedy Jenks is an engineering and consulting firm based in San Francisco, California, with a focus on water and industrial projects. Established in 1919, the company has developed a robust portfolio of services that includes wastewater treatment, water treatment, design engineering, and natural resource management. They cater to a variety of clients, including public agencies and private enterprises, demonstrating a commitment to innovative and sustainable infrastructure solutions. Kennedy Jenks has been involved in numerous significant projects, such as the EchoWater Project and various initiatives addressing PFAS contamination. Their approach combines sound engineering principles with a dedication to reducing costs and enhancing operational efficiency. The firm prides itself on its ability to listen to client needs and tailor solutions accordingly, fostering long-term relationships and repeat business. With a workforce of over 500 employees, Kennedy Jenks continues to play a vital role in the water treatment sector, adapting to the evolving demands of the industry.

3. Applied Membranes Inc.

• Website: appliedmembranes.com
• Ownership type: Private
• Headquarters: Vista, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Founded year: 1983
• Headcount: 201-500
• LinkedIn: applied-membranes-inc

Applied Membranes Inc. is a private company based in Vista, California, that has been manufacturing water treatment solutions since 1983. The company specializes in reverse osmosis systems and membrane elements, catering to a variety of industries including agriculture, pharmaceuticals, and beverage production. With a workforce of around 52 employees, Applied Membranes operates primarily through direct sales and distribution channels, ensuring that customers receive high-quality service and support. Their product range includes not only membrane elements but also water filters, pressure vessels, and ultraviolet disinfection systems. The company prides itself on its technical expertise and has a history of innovation in membrane technology, having been founded by Dr. Gil Dhawan, who has over 50 years of experience in the field. Applied Membranes is recognized for its commitment to quality and customer satisfaction, with thousands of their systems in operation worldwide.

4. Pure Aqua, Inc.

• Website: pureaqua.com
• Ownership type: Private
• Headquarters: Santa Ana, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Founded year: 2002
• Headcount: 11-50
• LinkedIn: pure-aqua-inc

Pure Aqua, Inc. is a water treatment company based in Santa Ana, California, specializing in the design and manufacturing of commercial and industrial water purification systems. Established in 2002, the company has built a reputation for providing engineered solutions that meet the specific needs of various industries requiring purified water. Their product offerings include a wide range of systems such as reverse osmosis (RO) systems, filtration solutions, and water disinfection products. With over 10,000 water purification systems installed globally, including 4,000 customized systems, Pure Aqua serves a diverse clientele across more than 200 countries. The company prides itself on its ability to generate over 500 million gallons of purified water daily, showcasing its operational capacity. All systems are engineered and manufactured in the USA, reflecting a commitment to quality and local production. Pure Aqua's expertise extends to various applications, including desalination, agriculture, and industrial processes, making it a significant player in the water treatment industry.

5. Puretec Industrial Water

• Website: puretecwater.com
• Ownership type: Private
• Headquarters: Oxnard, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Founded year: 1966
• Headcount: 51-200
• LinkedIn: puretec-industrial-water

Puretec Industrial Water, based in Oxnard, California, has been a prominent player in the water treatment industry since its inception in 1966. The company specializes in providing high purity water solutions tailored to the needs of various sectors, including power generation, pharmaceuticals, food and beverage, and microelectronics. Their services include deionized water tank delivery, industrial reverse osmosis systems, and water softening solutions. Puretec's innovative approach includes offsite regeneration of ion exchange resins, ensuring that clients receive high-quality deionized water without the hassle of onsite chemical handling. With a workforce of around 80 employees, Puretec prides itself on its customer service, boasting a 98% customer satisfaction rating. The company operates multiple facilities across the Southwestern United States, allowing for rapid response and support for its clients' water treatment needs.

6. Trussell

• Website: trusselltech.com
• Ownership type: Private
• Headquarters: Pasadena, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Founded year: 2003
• Headcount: 11-50
• LinkedIn: trussell-technologies-inc

Trussell, based in Pasadena, California, is an environmental engineering firm that specializes in providing comprehensive water treatment solutions. Founded in 2003 by Dr. Rhodes Trussell, the company has grown to employ between 11 and 50 professionals, all dedicated to tackling complex water quality issues. Trussell offers consulting services across various domains, including water reuse, drinking water, wastewater treatment, and desalination. Their clientele primarily consists of municipal agencies and organizations that require expert guidance in regulatory compliance and innovative water management strategies. The firm has been involved in notable projects such as the San Diego Pure Water Program and the Pure Water Monterey Advanced Water Purification Facility, showcasing their capability in implementing advanced treatment systems. Trussell's approach combines technical expertise with practical solutions, ensuring that they meet the evolving needs of the water treatment industry while maintaining a focus on sustainability and safety.

7. Seaco Technologies

• Website: seacotech.com
• Ownership type: Private
• Headquarters: Bakersfield, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Founded year: 1989
• Headcount: 51-200
• LinkedIn: seaco-technologies

Seaco Technologies, Inc. is a private company based in Bakersfield, California, founded in 1989. It specializes in providing tailored water treatment and dust control solutions to various industries, including agriculture, food processing, and industrial sectors. The company focuses on enhancing water quality and ensuring compliance with environmental regulations. Seaco's offerings include a wide range of water treatment systems, such as those for boilers, cooling towers, drinking water, and wastewater management. They also provide specialized products and services, including chlorination and sanitation solutions. With a commitment to customer service and a customized approach to problem-solving, Seaco Technologies has built a reputation for effectively addressing the unique challenges faced by its clients. The company operates primarily in the United States, with additional locations in Texas and Peru, showcasing its operational reach.

8. Chem Pro Laboratory

• Website: chemprolab.com
• Ownership type: Private
• Headquarters: San Diego, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Founded year: 1964
• Headcount: 11-50
• LinkedIn: chem-pro-laboratory

Chem Pro Laboratory, also known as Chem Pro LLC, is a private water treatment service provider based in San Diego, California. Founded in 1964, the company has built a solid reputation over its 50-plus years of operation, focusing on delivering comprehensive water treatment solutions for commercial, industrial, and institutional clients. Chem Pro's services are designed to meet the specific needs of various industries, ensuring compliance with stringent water quality regulations. The company prides itself on its high standards of service and its ability to adapt its treatment technologies to different applications. With a dedicated team of approximately 22 employees, Chem Pro operates primarily within California, positioning itself as a key player in the local water treatment market.

9. HydroScience Engineers

• Website: hydroscience.com
• Ownership type: Private
• Headquarters: Sacramento, California, United States (USA)
• Employee distribution: United States (USA) 82%, Vietnam 14%, Myanmar 4%
• Founded year: 1997
• Headcount: 11-50
• LinkedIn: hydroscience-engineers

HydroScience Engineers, founded in 1997 and based in Sacramento, California, is a private civil engineering firm that specializes in water, wastewater, and recycled water projects. With a team of dedicated professionals, including civil, mechanical, and electrical engineers, HydroScience provides a full suite of services that cover planning, design, and construction phases for water-related projects. Their portfolio includes the design of groundwater and surface water treatment plants, pump stations, and water distribution systems. They have successfully completed numerous projects, such as the Cache Creek Wastewater Treatment Facility and the Hollister Domestic Wastewater Treatment Facility Improvements, showcasing their ability to manage complex projects while ensuring regulatory compliance. HydroScience's commitment to high-quality engineering services has made them a reliable partner for both public and private clients in addressing critical water management needs.

10. H2O Engineering, Inc.

• Website: h2oengineering.com
• Ownership type: Corporate
• Headquarters: San Luis Obispo, California, United States (USA)
• Employee distribution: United States (USA) 76%, India 24%
• Latest funding: October 2022
• Founded year: 2000
• Headcount: 11-50
• LinkedIn: h2o-engineering-inc-

H2O Engineering, Inc., based in San Luis Obispo, California, is a water treatment company that has been operational since 2000. The firm specializes in providing customized solutions for a variety of sectors, including industrial, agricultural, and municipal clients. Their product lineup features advanced technologies such as filtration systems, chemical treatments, and ozone remediation, all aimed at optimizing water management and ensuring compliance with environmental regulations. H2O Engineering prides itself on its ability to tailor solutions to meet the specific needs of its clients, which is supported by a robust service offering that includes free water sampling, system design, equipment supply, and ongoing maintenance contracts. The company has a notable presence in the water treatment industry, with a workforce that includes employees in both the United States and India, reflecting a commitment to operational efficiency and global reach.

11. AXEON Water Technologies

• Website: axeonwater.com
• Ownership type: Private
• Headquarters: Temecula, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Founded year: 1989
• Headcount: 51-200
• LinkedIn: axeon-water-technologies

AXEON Water Technologies, based in Temecula, California, is a private company that has been operational since 1989. Specializing in water treatment, AXEON manufactures a wide array of filtration and purification systems, including advanced reverse osmosis and ultrafiltration systems. Their product offerings cater to a variety of sectors, including residential, commercial, and industrial markets. The company prides itself on delivering high-quality solutions and providing technical support to ensure that customers receive safe and clean water for their specific applications. With a workforce of around 34 employees, AXEON has successfully completed numerous projects and supplied a significant number of commercial and industrial systems annually. Their focus on innovation and customer service has positioned them as a trusted partner in the water treatment industry.

12. Aqua Metrology Systems Limited

• Website: aquametrologysystems.com
• Ownership type: Private
• Headquarters: Sunnyvale, California, United States (USA)
• Latest funding: Other (Debt), $500,000, December 2024
• Founded year: 2010
• Headcount: 11-50
• LinkedIn: aqua-metrology-systems-limited

Aqua Metrology Systems Limited, founded in 2010 and based in Sunnyvale, California, specializes in water treatment and environmental monitoring solutions. The company provides advanced instruments and treatment systems designed to ensure compliance with health and environmental standards for both municipal and industrial clients. Their innovative technologies, such as the THM-100™ online analyzer and SafeGuard™ H2O system, help optimize water treatment processes while reducing operational costs. Aqua Metrology Systems is dedicated to enhancing water quality through real-time monitoring and intelligent treatment solutions, addressing contaminants like disinfection by-products and trace metals. The company has recently secured funding, indicating its active role and growth potential in the water treatment sector.

13. D & H Water Systems, Inc.

• Website: dandhwatersystems.com
• Ownership type: Private
• Headquarters: Oceanside, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Founded year: 2005
• Headcount: 11-50
• LinkedIn: d-%26-h-water-systems-inc-

D & H Water Systems, Inc. is a manufacturers representative firm based in Oceanside, California, established in 2005. The company specializes in providing solutions for municipal water and wastewater markets, primarily in southern California and southern Nevada. Their offerings include chemical feed systems, wastewater management, and technologies aimed at improving water quality and efficiency. D & H Water Systems emphasizes customer service and technical expertise, aiming to be a valuable resource for end users, consulting engineers, and contractors. They actively engage in presenting new technologies and product advancements through demonstrations and presentations, showcasing their commitment to innovation in the water treatment sector. The firm has not reported any funding, indicating a self-sustained operational model.

14. Clear Creek Systems

• Website: clearcreeksystems.com
• Ownership type: Private
• Headquarters: Bakersfield, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Founded year: 1994
• Headcount: 51-200
• LinkedIn: clear-creek-systems

Clear Creek Systems, based in Bakersfield, California, has been a player in the water treatment industry since its founding in 1994. The company specializes in the treatment of stormwater, groundwater, and industrial process water, offering a variety of services including PFAS remediation, industrial flushing, and construction stormwater management. With a workforce of approximately 74 employees, Clear Creek Systems has developed a reputation for delivering tailored solutions that meet the specific needs of their clients. They have worked with a range of stakeholders, from engineering firms to government entities, showcasing their adaptability and expertise. Their innovative approach to PFAS treatment, utilizing advanced resins alongside traditional methods, positions them as a forward-thinking entity in the sector. Clear Creek Systems operates multiple locations across the United States, allowing them to engage in projects nationwide and maintain a strong presence in the water treatment market.

15. Trevi Systems

• Website: trevisystems.com
• Ownership type: Venture Capital
• Headquarters: Rohnert Park, California, United States (USA)
• Employee distribution: United States (USA) 80%, Oman 20%
• Latest funding: Series E-K, $10.0M, April 2020
• Founded year: 2010
• Headcount: 11-50
• LinkedIn: trevi-systems

Trevi Systems Inc. is a technology company based in Rohnert Park, California, founded in 2010. The company specializes in sustainable water purification and desalination solutions, particularly through its innovative forward osmosis technologies. Trevi Systems aims to provide clean water for various industries, including agriculture and energy, while emphasizing environmental sustainability and resource recovery. With a team of experienced scientists and engineers, Trevi has developed patented technologies that allow for low-energy desalination and brine concentration. The company has established pilot projects in locations such as Hawaii and Oman, showcasing its ability to deliver effective solutions in challenging water conditions. Trevi Systems has also secured significant funding, with a recent Series E-K round raising $10 million in April 2020, reflecting strong investor interest in their sustainable approach to water treatment.

16. Coombs-Hopkins Company

• Website: coombshopkins.com
• Ownership type: Private
• Headquarters: Carlsbad, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Founded year: 1984
• Headcount: 11-50
• LinkedIn: coombs-hopkins-company

Coombs-Hopkins Company, founded in 1984 and based in Carlsbad, California, specializes in water and wastewater treatment solutions. With a dedicated team of 25 employees, the company has built a strong presence in the western United States, providing essential equipment and systems to municipalities and water treatment facilities. Their portfolio includes a variety of projects, such as the Civic Center Water Treatment Facility in Malibu and the Turlock Regional Water Quality Control Center, showcasing their expertise in managing complex water treatment challenges. Coombs-Hopkins is committed to partnering with clients, engineers, and contractors to deliver effective treatment solutions that meet the evolving needs of the industry. Their long-standing experience and focus on quality make them a reliable choice for water management solutions.

17. Hydranautics - A Nitto Group Company

• Website: membranes.com
• Ownership type: Private
• Headquarters: San Diego, California, United States (USA)
• Employee distribution: United States (USA) 65%, India 16%, Brazil 3%, Other 17%
• Founded year: 1963
• Headcount: 501-1000
• LinkedIn: hydranautics

Hydranautics - A Nitto Group Company, based in San Diego, California, is a prominent player in the membrane technology sector, focusing on water treatment solutions. Established in 1963, the company has built a reputation for manufacturing high-performance membrane products, including reverse osmosis, nanofiltration, ultrafiltration, and microfiltration membranes. These products cater to various applications, from municipal water supply to agricultural irrigation and pharmaceutical processes. Hydranautics operates globally, supported by a network of offices and warehouses, ensuring timely technical and customer service. The company is dedicated to research and development, continuously innovating to meet the evolving demands of the water treatment industry. Their commitment to quality is reflected in their ISO 9001 certification, and they have a strong emphasis on customer support, providing end-to-end assistance from system design to maintenance.

18. Aquacycl

• Website: aquacycl.com
• Ownership type: Venture Capital
• Headquarters: Escondido, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Latest funding: April 2024
• Founded year: 2016
• Headcount: 11-50
• LinkedIn: aquacycl

Aquacycl, based in Escondido, California, is a wastewater treatment company that specializes in innovative solutions for managing industrial wastewater. Founded in 2016, the company has developed unique products like BETT® (BioElectrochemical Treatment Technology) and SulfideFix, which cater to industries such as food and beverage, hydrocarbon remediation, and manure management. Aquacycl's systems are designed to treat high-strength wastewater efficiently, ensuring compliance with environmental regulations while also reducing operational costs. Their services include custom solutions tailored to client needs, and they have garnered positive feedback from clients, including significant corporations like PepsiCo. The company operates with a focus on sustainability, aiming to minimize greenhouse gas emissions and promote water reuse. With a team of 31 employees, Aquacycl is positioned to make a meaningful impact in the water treatment industry.

19. King Lee Technologies

• Website: kingleetech.com
• Ownership type: Private
• Headquarters: San Diego, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Founded year: 1977
• Headcount: 11-50
• LinkedIn: king-lee-technologies

King Lee Technologies, founded in 1977 and based in San Diego, California, is a private company that specializes in water treatment solutions, particularly in membrane technology and chemical manufacturing. With a workforce of 11-50 employees, the company has carved out a significant niche in the industry by offering a range of products, including antiscalants, membrane cleaners, and RO system components. Their services extend to membrane studies and cleaning, which are vital for system operators and engineering firms looking to enhance water purification processes. Over the years, King Lee has built a reputation for providing effective chemical solutions and valuable insights into system optimization, making them a trusted partner in both public and private sectors. Their commitment to innovation is evident in their proprietary software, Hydracalc, which aids in chemical dosing and system management. This focus on customer service and technical expertise positions King Lee Technologies as a noteworthy entity in the water treatment field.

20. AqueoUS Vets

• Website: aqueousvets.com
• Ownership type: Private Equity
• Headquarters: Redding, California, United States (USA)
• Employee distribution: United States (USA) 100%
• Latest funding: January 2022
• Founded year: 2015
• Headcount: 51-200
• LinkedIn: aqueous-vets

AqueoUS Vets, based in Redding, California, is a water treatment solutions provider that specializes in engineering and construction services for water and wastewater management. Established in 2015, the company has built a reputation for delivering effective water treatment solutions tailored to the needs of both government agencies and private sector clients. Their product offerings include filtration equipment, chemical feed systems, and various appurtenances essential for water distribution and treatment. AqueoUS Vets also provides comprehensive services such as construction, equipment maintenance, and dewatering. The company prides itself on its technical expertise, with a leadership team that boasts over 150 years of combined experience in the water and wastewater industry. Their projects often focus on addressing critical issues like PFAS contamination, showcasing their commitment to innovative solutions in water treatment.

21. Garratt-Callahan Company

• Website: garrattcallahan.com
• Ownership type: Family Owned
• Headquarters: Burlingame, California, United States (USA)
• Employee distribution: United States (USA) 99%, Other 1%
• Founded year: 1904
• Headcount: 201-500
• LinkedIn: garratt-callahan-company

Garratt-Callahan Company, based in Burlingame, California, has been a prominent player in the water treatment industry since its inception in 1904. As a family-owned business, it has maintained a strong commitment to providing industrial water treatment solutions across various sectors, including healthcare, food and beverage, and manufacturing. The company offers a comprehensive range of services, including boiler water treatment, wastewater treatment, cooling water treatment, and reverse osmosis. Their analytical laboratory services ensure that clients receive accurate assessments of their water quality. With a focus on water safety and compliance, Garratt-Callahan helps clients navigate the complexities of water management, particularly in light of increasing regulatory scrutiny. Their expertise extends to addressing issues such as Legionella and other waterborne pathogens, showcasing their proactive approach to water safety. The company prides itself on building long-term relationships with clients, emphasizing trust and integrity in its operations. With a workforce of over 400 employees, Garratt-Callahan is well-equipped to meet the needs of its clients and adapt to the evolving challenges in the water treatment industry.

Water Treatment Insights: Key Companies in California

Company	Headquarter	Size	Founded	Ownership
Brown and Caldwell	Walnut Creek, California, United States (USA)	1001-5000	1947	Private
Kennedy Jenks	San Francisco, California, United States (USA)	201-500	1919	Corporate
Applied Membranes Inc.	Vista, California, United States (USA)	201-500	1983	Private
Pure Aqua, Inc.	Santa Ana, California, United States (USA)	11-50	2002	Private
Puretec Industrial Water	Oxnard, California, United States (USA)	51-200	1966	Private
Trussell	Pasadena, California, United States (USA)	11-50	2003	Private
Seaco Technologies	Bakersfield, California, United States (USA)	51-200	1989	Private
Chem Pro Laboratory	San Diego, California, United States (USA)	11-50	1964	Private
HydroScience Engineers	Sacramento, California, United States (USA)	11-50	1997	Private
H2O Engineering, Inc.	San Luis Obispo, California, United States (USA)	11-50	2000	Corporate
AXEON Water Technologies	Temecula, California, United States (USA)	51-200	1989	Private
Aqua Metrology Systems Limited	Sunnyvale, California, United States (USA)	11-50	2010	Private
D & H Water Systems, Inc.	Oceanside, California, United States (USA)	11-50	2005	Private
Clear Creek Systems	Bakersfield, California, United States (USA)	51-200	1994	Private
Trevi Systems	Rohnert Park, California, United States (USA)	11-50	2010	Venture Capital
Coombs-Hopkins Company	Carlsbad, California, United States (USA)	11-50	1984	Private
Hydranautics - A Nitto Group Company	San Diego, California, United States (USA)	501-1000	1963	Private
Aquacycl	Escondido, California, United States (USA)	11-50	2016	Venture Capital
King Lee Technologies	San Diego, California, United States (USA)	11-50	1977	Private
AqueoUS Vets	Redding, California, United States (USA)	51-200	2015	Private Equity
Garratt-Callahan Company	Burlingame, California, United States (USA)	201-500	1904	Family Owned

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