SAN CRISTÓBAL DE LAS CASAS, Mexico — Maria del Carmen Abadía lives in one of Mexico’s rainiest regions, but she has running water only once every two days. When it does come, the water is so heavily chlorinated, she said, it’s undrinkable.

Potable water is increasingly scarce in San Cristóbal de las Casas, a mountain town in the southeastern state of Chiapas where some neighborhoods have running water just a few times a week, and many households are forced to buy extra water from tanker trucks.

So, many residents drink Coca-Cola, which is produced by a local bottling plant, can be easier to find than bottled water and is almost as cheap.

In a country that is among the world’s top consumers of sugary drinks, Chiapas is a champion: Residents here drink on average more than two liters of soda a day.

The effect on health has been devastating. The mortality rate from diabetes in Chiapas increased 30 percent between 2013 and 2016, and the disease is now the second-leading cause of death in the state after heart disease, claiming more than 3,000 lives every year.

«When I was a kid and used to come here, Chamula was isolated and didn’t have access to processed food,» said Vicente Vaqueiros, a doctor at the clinic in San Juan Chamula, a nearby farming town. «Now, you see the kids drinking Coke and not water. Right now, diabetes is hitting the adults, but it’s going to be the kids next. It’s going to overwhelm us.»

Residents have identified what they believe is the singular culprit: the Coca-Cola factory on the edge of town.

The plant has permits to extract more than one million liters of water a day as part of a decades-old deal with the federal government.

Coca-Cola executives and some experts say the company has been unfairly maligned. They blame rapid urbanization, poor planning and a lack of government investment that has allowed the city’s infrastructure to crumble.

Climate change, scientists say, has also played a role in the failure of artesian wells that sustained San Cristóbal for generations.

«It doesn’t rain like it used to,» said Jesús Carmona, a biochemist at the local Ecosur scientific research center. «Almost every day, day and night, it used to rain.»

The plant is owned by Femsa, a food and beverage behemoth that owns the rights to bottle and sell Coca-Cola throughout much of Latin America. Femsa executives say the plant has little impact on the city’s water supply, noting that its wells are far deeper than the springs that supply local residents.

The company is also an important economic force, employing about 400 people and contributing around $200 million to the state economy.

Critics, however, say the deal between Femsa and the federal government doesn’t serve the city well.

«Coca-Cola is abusive, manipulative,» said Martin López López, a local activist. «They take our pure water, they dye it and they trick you on TV saying that it’s the spark of life. Then they take the money and go.»

Laura Mebert, a social scientist at Kettering University in Michigan, says Coca-Cola pays a disproportionately small amount for its water privileges, about 10 cents per 1,000 liters.

«Coca-Cola pays this money to the federal government, not the local government,» Ms. Mebert said, «while the infrastructure that serves the residents of San Cristóbal is literally crumbling.»

Among the issues facing the city is a lack of wastewater treatment, meaning that raw sewage flows directly into local waterways. Mr. Carmona said San Cristóbal’s rivers were rife with E. coli and other infectious pathogens.

Since bottles of Coca-Cola arrived here a half-century ago, the beverage has been deeply intertwined with the local culture. In San Juan Chamula, bottled soda anchors religious ceremonies cherished by the city’s indigenous Tzotzil population. Many Tzotzil believe carbonated soda has the power to heal the sick.

Local health advocates say marketing campaigns by Coke and Pepsi that started in the 1960s helped embed sugary soft drinks into local religious practices. For decades, the companies produced billboards in local languages, often using models in traditional Tzotzil outfits. Coke has since discontinued the campaigns.

Ms. Abadía said she blamed herself for drinking so much soda. Still, with her mother’s health deteriorating, and having watched her father die from complications from diabetes, she can’t help but fear for her own well-being.

«I’m worried I’ll end up blind or without a foot or a hand,» she said. «I’m very scared.»

A bottling plant brings jobs, and health problems.

© 2018 The New York Times