Building Local Supplies

Native plant garden weymouth

Think Regional, Act Local

Metropolitan was born out of the need to import water from hundreds of miles away to support a growing region. But as Southern California has evolved, so too has Metropolitan. Today, we are far more than just water importers. We are builders and planners, making large-scale investments in local supplies to complement our imported supplies. Our support of conservation, water-use efficiencies and diverse local resource programs like water recycling, desalination, groundwater recovery and storage have provided close to over 78 million acre-feet to the region’s resource mix, greatly increasing our resiliency and reliability. And we’ve only just begun. Metropolitan is in the process of developing what could be the largest water recycling facility in the world – Pure Water Southern California.

It’s not an either-or situation -- we’re developing local resources and shoring up our imported supplies. Each piece of our supply portfolio depends on the other. One insures us against the other’s vulnerabilities. When imports are challenged by drought cycles or natural disasters, local resources and conservation programs can help meet regional demands. In turn, high-quality imported supplies are necessary for recycling and groundwater replenishment programs. Working together, these sources provide Southern California with reliable water. Having access to a mix of water resources has protected the region from the impacts of drought cycles, climate change and extreme weather.

El Toro Water District Recycled Water Expansion

Local Supplies for Regional Reliability

When a local supply is developed -- whether it is in Ventura, San Diego, or any community in between -- all Southern California benefits. Our regional cooperation and interdependence mean one community’s recycling or groundwater cleanup project decreases the burden on Metropolitan’s imported supplies as a whole. That reduces operating costs, frees up conveyance capacity to benefit all system users and helps the region adapt to climate change. That is why Metropolitan supports and incentivizes several beneficial programs and initiatives that help the region develop local supplies and conserve. We have invested $1.6 billion in these programs to date. For a rundown synopsis of achievements, click here and for the full Achievement Report in Conservation, Recycling and Groundwater Recharge click here.

Metropolitan’s Local Resources Program provides incentives for member and local agencies to develop new local projects, such as water recycling and groundwater recovery. Metropolitan has provided financial assistance to more than 100 projects across Southern California, producing over 1.3 trillion gallons of recycled water and recovered groundwater. The value of regional reliability is elevated today in the face of critical shortages in the two main sources of imported water supplies. By providing direct funding based on how much water projects produce, the program has significantly increased their economic viability.

The numbers tell a success story. In the 1990s, nearly 60 percent of Metropolitan’s supply portfolio was water imported from the Colorado River and the State Water Project. The balance was from local resources. A shift in the supply paradigm model shows a 2035 mix of about 36 percent imported supply and 64 percent local resources.

Local Supply Target

Local Resources

Ensuring reliable water for Southern California requires investing in local water supplies from diverse sources along with widespread conservation.

An unusual rushing LA River.


Each year, about 1.1 million acre-feet of rainfall and stormwater flows are captured and recharged into local groundwater basins. As drought conditions continue and climate change continues to take hold, there is a growing interest in developing additional water supply through stormwater capture and use. In response, Metropolitan launched two pilot programs to better understand the costs and benefits of stormwater capture, yield and use in 2020. One program looks at opportunities to capture additional stormwater for direct use. The other explores additional stormwater capture for groundwater recharge. Together, Metropolitan has committed $12.5 million to these programs. The data collected will help us evaluate the water supply benefits of stormwater capture and provide the framework for future funding strategies.

Future Supply Actions

Metropolitan also is investing in research to develop future local water supplies through innovative approaches. Through the Future Supply Actions Funding Program, Metropolitan co-funds member agency pilot projects and technical studies aimed at increasing the potential of recycled water, stormwater, groundwater and seawater desalination. Metropolitan has so far invested $6.5 million in more than two dozen studies. Program goals include:

  1. Reducing barriers to future resource production
  2. Providing results that are unique, yet transferable
  3. Advancing the field of knowledge
  4. Targeting critical paths to water resource implementation

Since the initial round of funding in 2013, Metropolitan has co-funded 34 pilot tests, demonstration studies and white papers. Study reports are available here.

A feasibility study examines cost-effective disinfection treatment to meet advanced water treatment regulations undertaken by the San Diego County Water Authority and subagency Padre Dam Municipal Water District.

Detail photo from the Fallbrook Groundwater Desalter Project.


Metropolitan has explored seawater desalination as a potential new supply since the 1960s, and we even developed and piloted our own thermal distillation technology.

While desalination technology has been used to treat and recover brackish groundwater for decades, the cost of treating seawater was not historically competitive with other resources. In the past 10 years, rapid improvements in membrane performance, energy recovery technology and process design have lowered seawater desalination costs, making it, in some cases, competitive with other new supply options.

Since 2001, Metropolitan has provided financial incentives for our member agencies to develop local seawater desalination projects, and seawater desalination became part of our Local Resources Program in 2014. Metropolitan is considering a new regional desalination facility as a possible addition to its drought action portfolio of projects.