Why Water Problems Outside Our Region Can Affect Our Water Supply

A damaged canal in the Central Valley may seem like a distant issue for Southern California residents. However, California’s water systems are deeply interconnected. A water problem hundreds of miles away can eventually affect the reliability and cost of the water delivered to local communities.

Southern California depends on a combination of local groundwater, recycled water, stored supplies, conservation, and imported water. Much of that imported water must travel through shared reservoirs, pumping plants, canals, aqueducts, and treatment facilities before reaching the region.

When one part of that system loses capacity or requires major repairs, the effects do not necessarily remain within the community where the problem began. Water agencies throughout the state may face repair costs, operational challenges, supply constraints, and pressure on future water rates.

Understanding this interconnected California water system helps explain why responsible water planning matters everywhere, not only within our own region.

California’s Water System Extends Across the State

California does not receive most of its water in the same places where most residents live.

The California Department of Water Resources explains that approximately 75% of the state’s rain and snow falls in watersheds north of Sacramento, while much of the demand is located farther south.

To address that geographic imbalance, California developed an extensive network of reservoirs, aqueducts, canals, pumping plants, power facilities, and pipelines that move water between regions.

The State Water Project extends more than 700 miles across California and includes reservoirs, pumping plants, hydroelectric facilities, canals, tunnels, and pipelines. It delivers water to communities, farms, and businesses from Northern California to Southern California.

Because so many communities rely on the same major facilities, California’s water system functions less like a collection of isolated local networks and more like one interconnected system.

Southern California Depends on Infrastructure Outside the Region

A significant portion of Southern California’s imported water travels through infrastructure located far outside the communities that eventually use it.

The Metropolitan Water District of Southern California receives water through both the State Water Project and the Colorado River Aqueduct. State Water Project supplies travel from Northern California through the Sacramento-San Joaquin Delta and then south through the California Aqueduct.

The State Water Project provides about 30% of the water used across Metropolitan’s Southern California service area on average, although that percentage can change depending on weather, available supplies, and operating conditions.

This means the reliability of Southern California’s water supply is partly connected to the condition of canals, reservoirs, pumps, and aqueducts located hundreds of miles away.

When those facilities are damaged or lose capacity, Southern California water agencies cannot simply ignore the problem because it occurred in another part of the state.

Central Valley Groundwater Overuse Provides a Powerful Example

One of the clearest examples of California’s interconnected water challenges can be found in the Central Valley.

Groundwater is stored in the spaces between underground soil, sand, gravel, and rock. When groundwater is pumped faster than rainfall, rivers, or managed recharge can replace it, underground water levels fall.

In some areas, excessive groundwater pumping causes underground sediment layers to compress. As those layers compact, the land above them sinks in a process known as land subsidence.

The California Department of Water Resources identifies groundwater pumping as a primary cause of subsidence along the California Aqueduct. Pumping often increases during extended droughts, when farms and communities have less access to surface water.

This is not simply a local land-management issue. Subsidence can damage the infrastructure that carries water to other parts of California.

How Sinking Land Can Damage an Aqueduct

Aqueducts depend on carefully engineered elevations and slopes to move large amounts of water.

When the land beneath one portion of an aqueduct sinks, the canal may no longer maintain the elevation profile it was designed to have. Some sections can lose carrying capacity, storage space, and operational flexibility.

The affected system includes both the federally owned San Luis Canal and the state-owned California Aqueduct. The San Luis Canal is a joint-use facility that carries water for the federal Central Valley Project and California’s State Water Project. The connected California Aqueduct serves as the backbone of the State Water Project.

According to the California Department of Water Resources’ California Aqueduct Subsidence Program, subsidence has already lowered portions of these canals and reduced their ability to move water as originally designed.

The problem could become dramatically worse if corrective work is not advanced over the coming years. Under projected 2043 climate and subsidence conditions, the State Water Project’s long-term average deliveries could be reduced by as much as 84% without operational changes or infrastructure improvements.

In practical terms, the aqueduct may remain physically present but become unable to carry nearly as much water as the communities, farms, and businesses connected to it need.

This reduced capacity could affect Central Valley water users as well as Southern California agencies that depend on the system for imported water.

Repairing the Canal Could Cost Nearly $4 Billion

Restoring the affected portions of the San Luis Canal and California Aqueduct will require an enormous infrastructure investment.

A January 2026 estimate from the California Department of Water Resources places the total capital cost at approximately $3.87 billion in 2024 dollars.

Approximately $2.25 billion of that estimate is associated with repairs to the San Luis Canal, the federally owned joint-use portion of the system. Another $1.62 billion is associated with the state-owned California Aqueduct.

These are preliminary planning estimates rather than final project costs. Depending on future designs, construction conditions, and other uncertainties, the Department of Water Resources estimates the actual cost could range from approximately $2.71 billion to $5.81 billion.

The repairs could involve raising canal liners and embankments, replacing bridges and check structures, modifying turnouts, relocating utilities, and correcting other facilities affected by the sinking ground.

This helps show why groundwater overuse in one region can eventually create multibillion-dollar consequences for water users throughout California.

Why Southern California May Share the Repair Costs

The State Water Project is operated as a shared system.

The California Department of Water Resources has long-term contracts with 29 local public water agencies that receive water from the project. These agencies are known as State Water Project contractors.

Under those agreements, contractors repay costs associated with constructing, operating, maintaining, and improving State Water Project facilities. They also help cover expenses related to labor, power, maintenance, infrastructure financing, and major rehabilitation projects.

Although the San Luis Canal is federally owned, it is operated by the California Department of Water Resources as a joint-use facility carrying both Central Valley Project and State Water Project supplies. The state-owned California Aqueduct begins immediately downstream and carries water farther south.

Because the two portions operate as a connected water-delivery system, repairing subsidence damage will require coordination among state, federal, and local partners.

Southern California water agencies that depend on State Water Project supplies may therefore be responsible for a portion of the costs associated with restoring the system. Those expenses become part of the broader cost of obtaining and delivering imported water.

How Infrastructure Problems Can Influence Water Rates

Water rates pay for much more than the water itself.

They help support treatment facilities, pipelines, pumping, electricity, testing, staffing, storage, debt payments, maintenance, environmental requirements, and major capital improvements.

When an imported water provider faces higher infrastructure costs, those expenses may be reflected in the rates charged to the local agencies purchasing that water. Local agencies must then account for those higher wholesale water costs when developing their own budgets and rates.

This does not mean one damaged canal will immediately cause a dramatic increase in a household’s water bill. Infrastructure costs are often financed and recovered over many years.

However, multiple repair projects, aging facilities, rising energy prices, new treatment requirements, and water supply investments can collectively place upward pressure on the cost of delivering reliable water.

The connection between distant infrastructure and local rates is one reason water agencies closely monitor planning decisions throughout the state.

Reduced Aqueduct Capacity Can Also Limit Water Supplies

The consequences are not limited to repair expenses.

If a canal or aqueduct cannot carry its intended amount of water, agencies have less flexibility to move supplies when they are available.

During a wet year, reduced capacity may limit the amount of water that can be transported south and placed into reservoirs or groundwater storage for future use. During a drought, the system may be less capable of delivering limited supplies to the communities that need them most.

The California Department of Water Resources warns that, without operational adaptations or infrastructure improvements, continued subsidence could reduce the State Water Project’s long-term average delivery capability by as much as 84% under projected 2043 conditions.

The Department of Water Resources and the U.S. Bureau of Reclamation are evaluating improvements to the San Luis Canal and California Aqueduct intended to restore lost capacity and protect future water deliveries.

Restoring the system is therefore not only about repairing concrete or raising canal banks. It is about preserving California’s ability to transport and store water during both wet and dry conditions.

Another Central Valley Canal Shows the Cost of Waiting

The Friant-Kern Canal provides another example of the damage subsidence can cause.

This federally owned canal delivers water to approximately 1 million acres of farmland and more than 250,000 residents in the San Joaquin Valley. In its middle section, land subsidence caused the canal to lose more than 60% of its original carrying capacity.

The first phase of the Friant-Kern Canal Middle Reach Capacity Correction Project was estimated to cost approximately $292 million and addressed only 33 miles of the 152-mile canal. California provided funding for a portion of the work even though the canal is a federal facility.

This project demonstrates how repairing a subsidence-damaged canal can require cooperation and funding from multiple levels of government. It also shows that addressing only one section of a canal can cost hundreds of millions of dollars.

Even if groundwater pumping is reduced, some subsidence may continue because underground sediment can keep compacting after water levels change. That makes preventing additional damage especially important.

Investing Early Can Prevent Greater Costs Later

Major water infrastructure projects are expensive, but delaying maintenance can make the eventual solution even more costly.

The current preliminary estimate for rehabilitating subsidence-damaged portions of the San Luis Canal and California Aqueduct is approximately $3.87 billion. Without improvements, however, the system could lose a substantial portion of its future water-delivery capability.

Regular monitoring can identify land movement, structural deterioration, declining capacity, and other warning signs before they result in a more serious failure.

The California Aqueduct Subsidence Program monitors groundwater levels and changes in ground elevation to better understand how subsidence is affecting the system. State officials are also taking steps to address groundwater pumping near vulnerable infrastructure because continued pumping could undermine the benefits of expensive canal repairs.

Early investment may allow agencies to complete improvements in phases instead of waiting until an emergency forces immediate and potentially more expensive action.

The same principle applies locally. Maintaining groundwater basins, pipelines, treatment facilities, and pumping systems today can help prevent larger supply disruptions and future repair costs.

Local Planning Cannot Eliminate Every Outside Risk

Southern California water agencies can make responsible decisions within their own communities.

They can responsibly manage groundwater, expand recycled water, repair local pipelines, invest in storage, encourage efficient water use, and maintain treatment facilities.

Those investments reduce local vulnerabilities and make communities more resilient.

However, local planning cannot completely eliminate risks created elsewhere. Southern California will continue to depend on regional and statewide systems for part of its water supply.

That is why local water leaders must participate in broader discussions involving the State Water Project, the Colorado River, the Sacramento-San Joaquin Delta, statewide groundwater management, and major infrastructure investments.

Decisions made in those areas can eventually affect local supply reliability and water costs.

Responsible Groundwater Management Protects Shared Infrastructure

The Central Valley example also demonstrates why sustainable groundwater management is important.

Groundwater is an essential resource, particularly during droughts. However, pumping it faster than it can be replenished can create permanent damage.

Once certain underground sediment layers compact, the lost groundwater storage capacity may not fully return even if water levels recover. The sinking land can also damage canals, levees, roads, bridges, pipelines, and other infrastructure.

California’s Sustainable Groundwater Management Act established a statewide framework for bringing critically overdrafted groundwater basins into long-term balance. Local groundwater sustainability agencies are responsible for developing and implementing plans based on the conditions within their basins.

Successful groundwater management can help protect local wells and communities while also reducing the risk of additional damage to infrastructure relied upon by the rest of the state.

Water Is a Shared System, and So Are the Consequences

It can be frustrating to learn that local communities may help pay for water problems that began somewhere else.

However, Southern California also benefits from this shared system.

The State Water Project allows water captured in Northern California to support communities and economic activity throughout the state. Shared reservoirs and aqueducts provide access to supplies that would not otherwise be locally available. Regional cooperation also gives water agencies more flexibility during droughts, emergencies, and periods of uneven precipitation.

A shared system creates shared benefits, but it also creates shared responsibilities.

Poor groundwater management in one region can damage an aqueduct used by millions of people. Aging infrastructure in another area can limit the amount of water available for storage. A major repair project can affect the budgets of agencies located far from the construction site.

These connections are why long-term water planning must extend beyond city and county boundaries.

Protecting Our Local Water Future Requires Regional Cooperation

Reliable water service depends on both strong local management and responsible statewide planning.

Southern California communities must continue investing in local groundwater, recycled water, conservation, storage, and infrastructure. At the same time, water leaders must remain involved in decisions affecting the larger systems that deliver imported water to the region.

The Central Valley’s subsidence problem demonstrates what can happen when groundwater use and infrastructure planning are not aligned. Local actions can eventually create statewide consequences.

By investing in sustainable groundwater management, maintaining shared infrastructure, and planning before a crisis occurs, California can protect the water systems that communities, farms, and businesses depend on.

Water may be managed by different agencies and used in different regions, but it remains part of one connected system. Protecting that system requires every region to recognize that the benefits and consequences are shared.

By staying informed and supporting responsible infrastructure investments, we can help build a more reliable and affordable water system for every community.