How Regional Water Partnerships Strengthen Southern California’s Water Supply

Joe Grindstaff
2 days ago
6 min read

Red pushpin marks San Diego on a blurred road map, with Harbor and Coronado visible.

Southern California’s water system has always depended on cooperation. Water moves across county lines, through shared pipelines, treatment plants, reservoirs, and regional distribution systems before reaching homes and businesses.

That interconnected system is becoming even more important as communities prepare for population growth, climate variability, rising infrastructure costs, and uncertainty surrounding imported water supplies.

A new long-term agreement between Eastern Municipal Water District and the San Diego County Water Authority offers an example of how regional water partnerships can strengthen Southern California’s water supply without immediately requiring the construction of an entirely new water system.

The agreement gives EMWD access to an additional water supply while allowing San Diego County to make more efficient use of investments it has already made. It also demonstrates how cooperation between public water agencies can benefit communities on both sides of a water transfer.

What Is the New EMWD Water Supply Agreement?

In April 2026, Eastern Municipal Water District and the San Diego County Water Authority announced a long-term water supply agreement.

Under the agreement, EMWD will gradually begin receiving up to 10,000 acre-feet of water annually. Two additional agreements approved in August will add 10-15% more for our member agencies. The agreement is expected to remain in place for 21 years.

EMWD is also securing an advance of approximately 30,000 acre-feet that can be delivered later. This additional water gives the district more flexibility to manage its supplies during dry periods, periods of higher demand, or other water supply challenges.

The agreement is significant because the two agencies collectively serve more than four million people in Riverside and San Diego counties. It represents more than a transaction between two organizations. It is part of a broader shift toward coordinated Southern California water management.

Why Does EMWD Need Additional Water Supplies?

EMWD serves nearly one million people across a 682-square-mile area in western Riverside County and northern San Diego County. It is also located in one of the fastest-growing regions in the country.

Population growth creates additional demand for drinking water, wastewater service, recycled water, and the infrastructure needed to support new homes and businesses.

EMWD does not rely on a single source to meet these needs. Its water supply portfolio includes imported water, local groundwater, recycled water, conservation, and investments intended to improve local water reliability.

The district’s 2025 Urban Water Management Plan evaluates anticipated water demands, available supplies, drought risks, and water supply reliability over the next 25 years.

The agreement with the San Diego County Water Authority adds another option to that portfolio. Having access to multiple water sources gives an agency greater flexibility when one source is reduced, becomes more expensive, or faces regulatory and environmental constraints.

Water supply diversification does not eliminate risk, but it helps prevent a community from becoming overly dependent on one reservoir, aqueduct, watershed, or imported water source.

How Will the Water Reach Riverside County?

One of the most important aspects of this Southern California water agreement is that it will use infrastructure that already exists.

Water deliveries will move through pipelines and treatment systems operated by the Metropolitan Water District of Southern California. This allows the agencies to implement the agreement without first constructing an entirely new regional conveyance system.

Major water infrastructure projects can take years or decades to plan, permit, finance, and construct. They can also cost billions of dollars.

Using existing water infrastructure allows the participating agencies to create value from facilities that customers have already helped fund. It can also reduce the construction costs, environmental disruption, and permitting challenges that would accompany a new pipeline or treatment plant.

This does not mean that Southern California can stop investing in infrastructure. Existing facilities still require maintenance, repairs, upgrades, and eventual replacement. However, making better use of the system already in place can be one of the fastest and most cost-effective ways to improve regional water reliability.

What Does San Diego County Receive From the Agreement?

A successful regional water partnership must benefit both sides.

San Diego County has invested heavily in developing a diversified water supply portfolio. That portfolio includes long-term water transfers, conservation, local projects, and desalinated seawater.

The Water Authority’s planning indicates that it has enough supply to meet projected regional demands, including during multiple dry years. The agreement allows the agency to make productive use of available water while generating revenue from investments that have already been made.

According to the agencies, the EMWD agreement is expected to generate approximately $74 million for the San Diego County Water Authority during the first five years, including upfront payments.

That revenue can help reduce financial pressure on the Water Authority and its member agencies. In turn, this may help limit the effect that fixed infrastructure and water supply costs have on San Diego County ratepayers.

EMWD gains access to a dependable water supply without carrying the full cost and delay of developing a new source independently. San Diego County receives revenue that helps support the regional system it has already built.

That shared benefit is what makes regional cooperation valuable.

How Can Water Transfers Improve Drought Preparedness?

Water transfers allow water to move to locations where it is needed and can be used effectively.

During wet years, an agency may have more water available than it immediately needs. During dry years, another agency may face reduced supplies or increased demand. Agreements established before an emergency can create flexibility for both situations.

EMWD’s advance of approximately 30,000 acre-feet is especially important in this context. The district can secure the water now and arrange for it to be delivered later when it may provide greater value.

This type of planning can strengthen drought preparedness by giving water managers another tool before shortages become severe.

However, water transfers should not replace conservation, recycled water, groundwater management, infrastructure maintenance, or the development of local supplies. A resilient water system needs all of these strategies working together.

The purpose of a regional transfer is not to create unlimited water. It is to manage the supplies Southern California has more strategically.

Regional Cooperation Can Help Control Costs

Water affordability is becoming one of the most important issues facing California water agencies.

Agencies must maintain aging infrastructure, comply with water quality standards, prepare for extreme weather, invest in new supplies, and serve growing communities. Each of those responsibilities carries a cost.

When agencies attempt to solve every problem independently, customers may end up paying for duplicate facilities, separate administrative systems, and projects that are more expensive than a shared regional solution.

Regional water partnerships can help agencies:

Use existing pipelines and treatment facilities more efficiently
Share the cost of major infrastructure
Reduce unnecessary duplication
Gain access to specialized expertise
Coordinate drought and emergency planning
Match available supplies with regional demand
Generate revenue from existing investments
Delay or avoid some new construction costs

Not every water supply challenge can be solved through a transfer. Agencies still need to evaluate long-term availability, water quality, delivery capacity, environmental requirements, and cost.

Nevertheless, the EMWD water supply agreement shows that collaboration can create options that would not be available to either agency acting alone.

Water Does Not Follow Political Boundaries

Residents often think of water service as a local issue because they receive a bill from a specific city or water district. The actual Southern California water system is much more interconnected.

The water serving one community may begin hundreds of miles away. It may pass through infrastructure owned by state, federal, regional, and local agencies before reaching the customer.

That means decisions made by one agency can affect communities far outside its immediate service area. It also means that cooperation between agencies can create regional benefits.

The new EMWD and San Diego County Water Authority agreement was made possible through coordination among multiple public water agencies and the use of Metropolitan’s regional infrastructure.

This is a practical example of why water governance and regional planning matter. Building a reliable water future requires agencies to look beyond their individual boundaries and consider how supplies and infrastructure can serve the broader region.

A Model for Southern California Water Management

Southern California will continue to face difficult questions about water availability, affordability, growth, infrastructure, and environmental protection.

There will not be one project or source that solves every problem.

Imported water will remain important, but it faces uncertainty. Local groundwater provides valuable storage and supply, but it must be managed sustainably. Recycled water and desalination can create additional local resources, but both require significant infrastructure and investment. Conservation reduces demand, but communities still need reliable supplies for homes, businesses, public health, and economic activity.

Regional water partnerships help connect these strategies.

The EMWD and San Diego County Water Authority agreement gives Riverside County another dependable supply, creates value from San Diego County’s existing investments, and uses infrastructure that is already in place.

Most importantly, it demonstrates that Southern California water agencies can accomplish more when they treat regional cooperation as a central part of water planning.

As climate conditions and water demands continue to change, agreements like this may become increasingly important. The future of Southern California’s water supply will depend not only on finding new water, but also on managing, sharing, and moving existing supplies more effectively.