For the Chavez family and many others in California’s fertile San Joaquin Valley, bottled water is the toilet paper of their coronavirus pandemic — an everyday necessity that vanished from supermarket shelves.

In the Navajo Nation, where about a third of the population lacks indoor plumbing, volunteers are creating public hand-washing stations by repurposing detergent bottles as makeshift faucets.

And Jessica Endicott, who lives in the tiny community of Turkey Creek in eastern Kentucky, said the virus has exacerbated distrust of the local water, which leaves her skin red and itchy every time she bathes.

Having plundered several major cities, the novel coronavirus is taking root in marginalized rural communities. Many of them lack clean water, making it impossible for residents to shelter at home or wash their hands frequently.

The pandemic is highlighting the yawning racial and ­socioeconomic disparities in access to clean water and intensifying calls for federal investment in the nation’s troubled water system. One festering public health problem is exacerbating a new, more acute one, experts say. The entire population is endangered when communities are left without a basic resource: safe water.

“If we do not extend services to people who do not have them, we cannot control the virus,” said Gail Brion, a professor of civil engineering at the University of Kentucky who is seeking funding to provide basic hygiene for homeless people. “You can’t have a truly healthy populace unless you serve every layer.”

Infection and death rates have ramped up in rural areas, particularly in the Deep South and other regions plagued by poverty. The Navajo Nation, for example, ranks close behind hot spots in the Northeast for infection rates.

“Nobody is thinking about these pockets of vulnerability,” said George McGraw, founder and chief executive of the nonprofit DigDeep who noted a “strong correlation” between the spread of the virus and communities that lack water.

According to a report released last year by DigDeep, in partnership with the U.S. Water Alliance, more than 2 million Americans do not have indoor plumbing. Far greater numbers do not believe that their water supplies are safe or cannot afford to pay for them.

The study found that black and Latino households are twice as likely as white households to lack a tap and a flushable toilet; among Native Americans, the chance of having to rely on an outhouse and a communal drinking-water source is 19 times higher.

Those groups are also more likely to suffer from diabetes, high blood pressure and obesity, which put people at a higher risk of developing severe complications from covid-19, the disease caused by the novel coronavirus.

“Water is tied up with other social determinants of health,” said McGraw, who has been tracking the virus as it shows up on Indian reservations, in the Deep South and in the colonias of El Paso, where he said deliveries of trucked water have dropped by 50 percent and some elderly and disabled people worry that younger family members who haul for them will get sick or lose their jobs, cutting them off from their supplies.

DigDeep, which brings water to underserved areas, temporarily halted a project providing cisterns to isolated homes in the Navajo Nation when the virus hit. Two clients died before their water tank was installed.

At least 14 states plus the District and Puerto Rico have ordered moratoriums on shut-offs during the crisis to ensure that residents can continue to cook, drink and wash their hands without leaving home. A few are reconnecting supplies.

Some experts hope the pandemic could ultimately prompt long-overdue investment in the country’s water system.

“Access to sanitation and hygiene is critical to public health all the time and especially now in addressing the crisis,” said Kristina Surfus, managing director of government affairs at the National Association of Clean Water Agencies, which has been calling for federal investment in the next stimulus legislation.

For now, though, lost jobs and factory closings are putting extra pressures on utilities.

“Covid-19 is having a significant negative impact on water utility revenue and households’ ability to pay,” Surfus said.

The virus has also placed additional strain on people who do not trust their water. In Porterville, Calif., Cristobal Chavez has long worried about polluted well water at his small family ranch, surrounded by dairy farmers and almond growers. His wife, Nora, who suffers from cancer, and his 19-year-old daughter, Cassandra, who had bouts of unexplained illness, wonder whether the water was to blame.

Now that the coronavirus has created shortages of bottled water, they have little choice but to drink from their well.

“But that makes it worse, that makes the nitrates worse,” said Cristobal, worrying that boiling might intensify any toxins.

In recent years, extended droughts in the region made wells run dry, elevating residents’ fear of shortages even as they are urged to wash their hands more frequently.

In nearby Visalia, Lucy Hernandez, a clean-water advocate, said panic buying quickly emptied the shelves at stores including Walmart and Costco. Hernandez, who uses bottled water for drinking and cooking, said supplies are now rationed, prompting more frequent trips to the store.

“We are only allowed to buy two gallons of water per customer,” said Hernandez, who has a household of five. “That only lasts one day in my house.”

Across the state in the Salinas Valley, Horacio Amezquita, general manager of the San Jerardo Cooperative, says he has seen prices for bottled water rise from 20 cents to 35 cents per gallon.

“Some people are taking advantage,” said Amezquita, who worries that elderly people, the homeless and undocumented workers will be hardest hit.

The migrant workers are just arriving to work in broccoli, cauliflower and strawberry fields, he said, many of them living three to a room and working on machines only three feet apart, making it easy to pass on the virus even if they wear masks and wash frequently.

Many policymakers fear that a next wave of infections will be among farmworkers who are considered essential employees but may not have time to wash their hands effectively, despite regulations from the Occupational Safety and Health Administration intended to guarantee safe working conditions.

“Those rules were never written with covid in mind,” said Scott Faber, senior vice president for government affairs at the Environmental Working Group.

The challenge of updating and expanding America’s network of more than 1 million miles of pipes is enormous. Many of those pipes are a century old — and have a 75-year life expectancy. In its quadrennial report card, the American Society of Civil Engineers gave America’s drinking-water system a D grade. The American Water Works Association estimates that it will take $1 trillion to support demand over the next 25 years.

Water is delivered to customers via more than 50,000 individual water departments, of which only about 400 serve big communities. The rest, spread across small towns, lack the economies of scale and technological expertise to upgrade systems. Millions more Americans rely on private wells with no means of monitoring water quality.

Less than 5 percent of the total budget for operations from infrastructure to water treatment comes from the federal government, according to data provided by the National Association of Clean Water Agencies. The rest comes from states and the revenue that utilities generate, which is threatened not only by growing unemployment but also by the closure of companies that use large amounts of water.

“It’s a question of priorities; water is at the most basic in terms of what people need to survive,” said Steve Fleischli, senior director for water at the Natural Resources Defense Council. He worries that the infrastructure and affordability problems will linger beyond the current crisis unless swift action is taken.

The novel coronavirus has proved susceptible to soap and water, and the standard treatment used by most municipal drinking-water systems should also inactivate it, according to the Centers for Disease Control and Prevention. But its traces have been found in human feces and untreated wastewater, leading scientists to investigate whether people might become infected through fecal transmission, although there has not been a confirmed report of the virus spreading that way.

“It’s an active area of research,” said Saurabh Mehandru, a gastroenterologist and laboratory scientist at Mount Sinai Hospital in New York who said scientists are looking into whether bile and other intestinal acids render the virus harmless.

All those factors worry Legena Wagner, who lives in a small family compound without indoor plumbing in sparsely populated Apache County, Ariz.

Her father, Timothy Tsosie, now leaves home before dawn to fill the family’s water containers, driving about 45 minutes along red-clay roads to the windmill pump before others crowd around waiting for their turn.

Wagner, who suffers from a rare inflammatory disorder that leaves her prone to infection, has moved out of the family home into a traditional Native American hogan to avoid sharing close quarters. She said the virus had strained their limited supplies.

She knows she should wash her hands under running water rather than in the decorative bowl on her kitchen counter, but she hates to see any precious liquid drain away. She washes clothes at home, rather than risking a trip to the laundromat. And many neighbors, she said, have been using well water for new plantings to avoid going to the supermarket.

“I think that water is going to become even more scarce than it has already been because farming and having your own garden is the way to be safer,” said Wagner, who is hoping that a water tank may one day be installed at the family property.

McGraw, of DigDeep, said the nonprofit had retooled its operations in the Navajo Nation, where more than 300,000 people live, and is back at work installing and refilling cisterns for isolated families like Wagner’s.

“These places are at greatest risk. If we let them stay that way, we are all at risk,” he said. “In today’s world, there’s no way we can contain that.”

Melina Mara in California contributed to this report.