Droughtsville, California, is in trouble.

Its water supply is endangered as multiple crises intensify: worsening droughts, competition for scarce supplies, sea level rise, groundwater contamination, earthquakes, wildfires and extreme weather. All of these factors, and more, threaten Droughtville’s ability to provide clean water to its residents. 

The city is fictional, but the threats are not.

A typical city in California faces multiple stressors that put drinking water supplies at risk — drought just happens to be the focus now. Huge volumes of water are transported hundreds of miles to Southern California and Bay Area cities via aqueducts. Other municipal water is stored underground in aquifers, potentially susceptible to contaminants and seawater invasion. And the intricate network of treatment plants and pipelines that carry water to people’s faucets is vulnerable to an array of natural and human-made threats.

CalMatters delved into the details of what scientists and planners have determined could jeopardize the water supply of a typical California city — and some potential solutions.


earthquake illustration
Credit: Illustration by Cecily Mireles

While scientists are still researching connections between water, climate change and seismic activity, the threat of earthquakes looms large in California. Damage to water sources and systems can reverberate from hundreds of miles away.

All it would take to inflict widespread damage on water systems is an earthquake of 6.0 magnitude or greater centered in the “right” place. Quakes of that magnitude can crack pipes, damage storage systems or release natural gas or oil into aquifers. 

Southern California’s reliance on water imported from outside the region puts its supplies at great risk from quakes. Parts of the Los Angeles Aqueduct, the California Aqueduct and the Colorado River Aqueduct — all of which bring water to Los Angeles — traverse the San Andreas Fault. A 7.8-magnitude quake on the fault would put the three aqueducts out of commission, cutting off some of the city’s water deliveries for as long as two years, according to a scenario evaluated by the city. Repairs could stretch out years. Because these aqueducts supply most of Southern California’s water, officials would have little choice but to impose mandatory water reductions.

Other examples:


wildfire illustration
Credit: Illustration by Cecily Mireles

Wildfires can directly harm water supplies, such as burning down storage structures and melting pipes, but also indirectly harm by sending up clouds of smoke and loosening soil, which washes debris and ash into watersheds. Wildfires even in remote parts of the state can pollute water that ends up in city taps.

  • Water samples collected from drinking water in Santa Rosa after the 2017 Tubbs and 2018 Camp Fires tested positive for benzene, a cancer-causing chemical. State water officials said the contamination most likely came from overheated pipe materials, as well as smoke and combustion byproducts.
  • Wildfires can lead to ash and sediment running off into water sources when it rains. The Mokelumne watershed, in particular, is at risk of this.
  • The 2015 Butte Fire burned a 12,000-acre section of a watershed, then winter storms carried debris from the fire into the river and reservoir. The US Geological Survey estimates likelihoods and magnitudes of such post-fire debris flows.
  • Water systems also depend on power to maintain operations, making them vulnerable to public safety power shutoffs and unplanned outages.

And then there are megafires: Super hot and dry conditions combine to create a complex of super-intense fires. In 2020 California experienced megafires that burned three Sierra Nevada watersheds important to California’s water supply. Runoff, erosion and sediment could occur near areas with moderate and high soil burn severity, although effects may not be seen for several years.


storm illustration
Credit: Illustration by Cecily Mireles

Large storms can overwhelm flood control channels and damage pipelines and other infrastructure. Rivers carry debris and sediment to reservoirs, where they can clog filtration systems, especially in burned areas. This was a concern in Fresno after the 2020 Creek Fire.

Storm surges and large volumes of rainfall can overwhelm unprepared city systems. An ARkStorm scenario, developed by the US Geological Survey, envisions a series of hurricane-level atmospheric rivers from the tropical Pacific slamming into the US West Coast over several weeks. Patterned after the Great Flood of 1861-1862, which put the Central Valley under as much as 15 feet of water, the ARkStorm scenario could flood thousands of square miles of urban and agricultural land, costing some $725 billion.

Chemical contaminants

chemical contaminants illustration
Credit: Illustration by Cecily Mireles

A variety of industrial chemicals contaminate drinking water supplies. “Forever chemicals” have polluted well water throughout California, most often near airports, military bases and landfills. These perfluorinated chemicals are linked to kidney cancer and other serious health conditions in people drinking contaminated water

Other examples of industrial contaminants found in water supplies are perchlorate from defense contractors and flame retardants from building materials.

In addition, copper, arsenic and other elements naturally found in soil can leach into groundwater and plumbing systems. From 2015 through 2018, 4,460 active drinking water sources were reported to contain arsenic. 
Lead, which can alter children’s brain function and trigger learning disabilities, mostly seeps into water from home pipes and faucets. EdSource created an interactive map for checking the lead levels in schools’ drinking water.

Urban runoff

urban runoff illustration
Credit: Illustration by Cecily Mireles

After rainstorms — particularly the “first flush” of California’s wet season — pollutants wash into streams and other surface waters. Stormwater and other urban runoff can deposit trash, oil, pesticides, fertilizers, sewage and sediment into streams that provide drinking water. 

The largest source of runoff in California is its more than 50,000 miles of highways. Caltrans is required by the state Water Resources Control Board to control stormwater runoff to the “maximum extent practicable.” As a result, Caltrans monitors runoff and takes steps to prevent contaminants from flowing off roads during rainstorms, such as preventing erosion and removing debris.

The state water board also regulates construction sites and industries through permits that require companies to develop plans to prevent runoff.

Nevertheless, anything that is dumped into a street or spread onto a lawn or garden can wind up in lakes, rivers and streams.

Stormwater runoff flows from roofs, yards and roads into storm drains.
Credit: Caltrans

Sewage spills

sewage spill illustration
Credit: Illustration by Cecily Mireles

Spills from sewage treatment plants and sewer lines contaminate surface waters with viruses, bacteria and other contaminants from wastewater that is flushed down drains and toilets.

For instance, flooding at the Hyperion Water Reclamation Plant in El Segundo in the summer of 2021 spilled 17 million gallons of sewage into Santa Monica Bay, contaminating beaches. But the spill also triggered water supply problems because local officials had to divert clean drinking water to uses, such as parks and golf courses, that were normally served by the recycled water treated at the Hyperion plant.

Rising sea levels and floods

sea level rise illustration
Credit: Illustration by Cecily Mireles

As the Arctic melts from global warming, oceans are rising. And this could cause saltwater to seep into coastal groundwater basins, requiring more treatment of drinking water. Rising sea levels also could increase storm surge flood events. Low-lying sewage treatment plants, such as in the Bay Area, are at risk of flooding as seas rise.

Large amounts of water dumped on a city in hours also can trigger major flooding, another key concern for water systems. In addition to direct infrastructure damage, such as levee failure, flooding can contaminate supplies and wash out water mains. Researchers mapped 440 hazardous facilities in California that could flood from sea level rise by 2100, disproportionately exposing lower-income communities of color to dangerous chemicals.


drought illustration
Credit: Illustration by Cecily Mireles

Lack of rainfall and snowpack stresses both of California’s main sources of drinking water: underground aquifers and surface water.

The 2021 water year (October 2020 to September 2021) was the state's second driest year on record and driest year since 1924 in terms of statewide precipitation, according to the California Department of Water Resources. Read more about the impacts of drought from CalMatters: ​​Running out of water and time: How unprepared is California for 2021’s drought?

During droughts, water deliveries are slashed for growers, urban residents and industry. Next year’s initial allocation from the State Water Project, the 700-mile system that channels water from Northern California rivers, is 0%. That means water agencies serving 27 million Californians and 750,000 acres of farmland can only expect water from the project if they require it for minimum health and safety needs.

“Parts of Southern California depend on this supply almost exclusively for their water. We are working…to make sure residents and businesses understand the severity and complexity of the situation and are responding by reducing their water use as much as necessary,” said Adel Hagekhalil, general manager of the Metropolitan Water District, which provides imported water to 19 million people in Los Angeles, Orange, Riverside, San Bernardino, San Diego and Ventura counties.

Reduced allocations from the massive state project are becoming the norm, not the exception: The last time there was a 100% allocation was in 2006.


hacker in computer illustration
Credit: Illustration by Cecily Mireles

Bad actors can target water supplies in different ways. Sometimes it’s a physical attack: In January 2021, a hacker tried to poison a Bay Area water treatment plant, according to reporting from NBC News.

But cybersecurity is increasingly important as more water systems rely on remote access to operators to control them. Ransomware attacks, where cybercriminals hold online systems hostage until victims pay a ransom, have already come for California schools and local governments. Water systems are potential targets to be taken offline.

When water systems detect a potential security breach or identify threats, they are supposed to consult with local law enforcement and report to the Water Information Sharing and Analysis Center.

Solutions: How are cities coping with these threats?

city emergency illustration
Credit: Illustration by Cecily Mireles

All of these threats to Droughtsville’s water supply are intimidating. So what can the city do to cope?

There are short-term coping mechanisms, such as mutual aid from surrounding areas and emergency proclamations. But there also are long-term ideas like building desalination plants and recycling, storing and capturing more water.

Mutual aid

first responders illustration
Credit: Illustration by Cecily Mireles

The state encourages public water systems to join a local or regional mutual aid organization, which can help find equipment and personnel after a disaster. For example, after a 2014 earthquake damaged water infrastructure in Napa, the California Water/Wastewater Agency Response Network (CalWARN) activated, allowing nearby utilities to assist with repairs. 

Water utilities may share information and infrastructure, and even supplies where needed. For example, Sacramento-area water agencies are collaborating on an underground “water bank” to be filled with excess water during wet years and used during dry years. 

A number of emergency tools become available at the local, state and national level:


Desalination can turn seawater or brackish water into drinking water. California has four seawater desalination facilities, with more proposed. Poseidon Water’s facility in Carlsbad, the largest in the Western Hemisphere, provides about 12% of water used in San Diego County. Common concerns include cost, energy required and environmental impacts.

Desalination’s high cost mainly stems from its enormous use of fossil fuels, which also emit greenhouse gases. Pipes taking in water can kill marine organisms as they take in water, as well as the brine that is discharged back into the environment. Researchers in California and around the world are studying how to lower costs and improve desalination technology.

How desalination works. Source: San Diego County Water Authority
How desalination works. Source: San Diego County Water Authority

Conserving more water

water conservation illustration
Credit: Illustration by Cecily Mireles

Even as the state suffers its second-driest year on record, Californians have not taken it very seriously: The governor requested a voluntary 15% cut in water use in July 2021, but since then  residents have reduced home water use by less than 4%.

During the last drought, Californians on average cut residential summer use by 30% between 2013 and 2016. Per capita water use has increased since 2016, but Californians used 14% less water on average in 2020 compared to 2014.
Without a statewide mandate or standardized water waste rules, California faces a patchwork of local water restrictions, with some areas imposing regulations while others have not.

Digging deeper wells

Groundwater makes up 40% of California's water supply, and in dry years that rises to 60%. The overwhelming majority of that groundwater — 79%, on average — goes to agriculture.

During the last drought, thousands of wells, mostly in poor farm communities in the Central Valley, went dry. But thousands of new wells are constructed every year, and existing wells are modified to increase pumping capacity. Depletion of groundwater is a growing concern, particularly in the central part of the state, as growers and others dig deeper and deeper wells.

A 2014 state groundwater law has had little to any effect on reducing depletion so far. Most local water suppliers are still working on their plans for how to regulate pumping. Six draft plans, mostly in the San Joaquin Valley, have been deemed insufficient and sent back by state water officials. The goal of the law is to make groundwater pumping sustainable within 20 years — a long time off when almost-back-to-back droughts are becoming the norm.

Capturing more stormwater

The Santa Monica pier in Santa Monica on March 25, 2020. REUTERS/Lucy Nicholson
The Santa Monica pier in Santa Monica on March 25, 2020. REUTERS/Lucy Nicholson

Stormwater runoff comes from rain that flows over impervious surfaces, such as streets and rooftops. If captured, it can be used or stored to recharge groundwater aquifers.

Cities historically managed stormwater to prevent floods. But in recent years, state and local policies are shifting to use it as a way to increase water supplies.

For example, Los Angeles County voters in 2018 passed Measure W, a property tax projected to raise hundreds of millions of dollars annually to capture and clean up stormwater. As part of that effort, Santa Monica is capturing 1.6 million gallons of runoff from its pier area, treating it and then using it for irrigation and toilet flushing.

The benefits to Santa Monica are twofold: It keeps polluted runoff off its beaches and provides usable water. 

Obstacles to capturing stormwater include inadequate funding, poor water quality and lack of regulations. Projects to capture, transfer and treat stormwater are often expensive and hard to put in place without grants and local bond measures.

Recycling more water

Water conservation signage at at Descanso Gardens in La Cañada Flintridge, on June 22, 2021. Photo by Pablo Unzueta for CalMatters
Water conservation signage at at Descanso Gardens in La Cañada Flintridge, on June 22, 2021. Photo by Pablo Unzueta for CalMatters

Recycled water is treated sewage. In most cases, it’s used for irrigation or recharging groundwater basins. San Jose operates a recycling system and distributes treated wastewater for non-potable purposes, such as agriculture; industrial cooling and processing; and irrigation of golf courses, parks and schools. 

The Orange County Water District has a longstanding, state-of-the-art project that recycles wastewater into drinkable supplies stored in its groundwater basin. It takes water that would've been discharged into the ocean and purifies it to drinking water standards. The water is then injected into the aquifer to replenish it for wells.

The Santa Clara Valley Water District plans to develop highly purified water for potable reuse by 2025.

Storing more water

Lake Oroville is one of California’s largest reservoirs for storing water. It has shrunk substantially in 2021. Image via NASA
Lake Oroville is one of California’s largest reservoirs for storing water. It has shrunk substantially in 2021. Image via NASA

Water suppliers have proposed more than 1,000 reservoirs in California to store water from surface rivers and streams. But they face uphill battles from the competing interests of environmentalists, farmers and city users. 

For instance, the controversial Sites Reservoir, proposed by a coalition of irrigation districts and the U.S. Bureau of Reclamation, could harm salmon and other fish in the Sacramento River and the Bay-Delta, according to state wildlife officials. Voters passed a $7.5 billion bond in 2014 to fund water projects such as the Sites Reservoir, which has been discussed since the 1950s. But none of the projects scheduled to receive that money have been built. Federal and state agencies are collecting public comments on the latest version of the Sites Reservoir project.

How can I learn more about my city’s water?

Look up your water supplier to learn more about contaminants or other information.

Much of the research for this report came from the State Water Board's Safe Drinking Water Plan for California, published in September 2021.

Many examples also came from Urban Water Management Plans. Under a 1983 law, large urban water suppliers must prepare and adopt a plan every five years to be eligible for state funding. Here are some examples:

John Osborn D'Agostino contributed to this explainer.

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Erica is a data reporter at CalMatters helping develop data-driven graphics and tools. As a California native, she is excited to contribute to important coverage of state issues through engaging projects....