Nanotechnology brings safer water to the Ganges Delta

By Kamala Thiagarajan

Growing up on the edge of the Ganges Delta in eastern India, Sajal Kanti Kayal understood from an early age that the most precious resource in the world was water. Here water comes in abundance. For six months of the year, it surges in from Himalayan snowmelt, monsoon rains, and tropical cyclones. But as it churns through the rivers of the state of West Bengal and neighboring Bangladesh on its way to the sea, that precious water picks up a dangerous payload.

“We’re surrounded by toxic water. Our ponds, canals, lakes — all polluted,” says Kayal. The 47-year-old is the founder and CEO of a charity that supports education, health care, and other local development in his home village of Kankura outside Kolkata. So he understands that clean water supports more than just public health. It can lift people out of poverty and increase the number of kids in schools. He knows this intimately. Over the years, he’s experienced hair loss, skin lesions, and frequent digestive upsets caused by tainted water.

“It’s a desperate situation,” he says. “There’s water everywhere, but not a drop to drink.”

Like many parts of the world, the region has surface water that is often contaminated by runoff, industrial pollution, and poor sanitation — a problem amplified by recurring floods. As a result, West Bengal has India’s highest share of waterborne diseases, particularly acute diarrheal diseases. Starting in the 1970s, officials encouraged people to drill what are known as tube wells into groundwater aquifers. But in a painful irony, that water too was contaminated with a deadly poison: arsenic.

The highly toxic element leaching into water is a widespread global issue, putting as many as 230 million people at risk, with most contamination arising from arsenic that is naturally found in rock and soil. It’s a particular problem in northeast India and Bangladesh, where experts once called the situation the largest mass poisoning in history. Long-term exposure causes a host of illnesses from skin lesions to cancer.

On the Indian subcontinent, rivers carry weathered rock from the Himalayas and deposit it as arsenic-rich sediment in the vast alluvial plains that stretch like a ribbon across northern India and Bangladesh. With no smell or taste, arsenic is undetectable in groundwater except through regular testing.

Several years ago, Arindam Roychowdhury, owner of a health care company in Kolkata, traveled to the remote subdistrict of Kakdwip, among the interwoven tidal channels and islands along the Bay of Bengal. He was dismayed by what he saw. “People had tied a rudimentary cloth filter over tube wells to keep the insects out of the water,” he says. “Villagers were consuming water from highly polluted ponds and using the same source of drinking water for washing clothes and utensils, as well as bathing. Some of these ponds were green, ridden with moss. The stomachs of the children I met were swollen like a bowl, and it was clear that there was immense suffering from waterborne illnesses.”

Roychowdhury, a member of the Rotary Club of Calcutta, wanted to help and knew his club, which focuses on service projects in health care, water and sanitation, and basic education and literacy, would be ready to join him.

An acquaintance at Tata Chemicals, a company specializing in the manufacture of chemical products for the pharmaceutical and other industries, told him about a filtration machine that employs a form of nanotechnology that is effective at destroying contaminants in water.

Because the systems use gravity-fed water pressure, they don’t require electricity, making them especially useful in rural areas with less reliable energy. The technology is affordable and scalable with systems designed for individual households and entire communities.

Tata Chemicals agreed to provide the water purifiers at a subsidized cost for the Rotary club’s project. After installing machines at four sites starting in 2022, the club received a $30,000 Rotary Foundation global grant in 2024 to install 10 additional purifiers at schools, nongovernmental organizations, and other public sites to allow community access.

While the purifiers are highly effective at eliminating bacteria and viruses from water, they are unable to remove more than a small amount of arsenic. So the club uses them in villages with lower levels of contaminants, as levels can vary greatly even among wells in the same area. Surplus amounts of clean water are then supplied to nearby villages for a nominal fee.

The project is directly benefiting an estimated 25,000 people. Each machine can filter 1,000 liters (264 gallons) of water per hour. Now, the members are looking to expand with another 21 filtration projects at schools.

The club’s international partner on the project is the Rotary Club of Colleyville, Texas, which also champions water and sanitation projects. The Colleyville club’s president and past Foundation chair, Kithsiri Athulathmudali, was experienced in clean water projects, particularly in his native Sri Lanka, which experiences similar water quality challenges.

“What defines us is Rotary’s Service Above Self mindset,” says Athulathmudali, a former Sri Lankan ambassador to Qatar. “We see what needs to be done, whether it is half a world away or in our own backyard, and we roll up our sleeves and do it.”

The Rotary Club of Calcutta received a Rotary Foundation global grant to install purifiers at schools and other public sites to allow community access. Courtesy of Arindam Roychowdhury 

Since 2013, Rotary clubs have led more than half a dozen global grant-supported projects to address arsenic contamination in India and Bangladesh.

The problem is not limited to less developed countries. In places like California’s agricultural heartland, residents, particularly in communities home to farmworkers, contend with water tainted by arsenic and fertilizer chemicals. There, too, arsenic is naturally occurring but can become more of a problem through excessive pumping of groundwater.

Globally, the issue remains a major public health problem without an easy solution beyond widespread testing and filtration, says Allan Smith, professor emeritus of epidemiology at the University of California, Berkeley and an expert on arsenic. “Methods for filtering arsenic have been around for a long time, but they do face problems,” he says. Downsides include the need for careful disposal of filters containing concentrated arsenic that must be treated as highly toxic waste. Even with filters, regular monitoring of water quality is needed and requires trained staff. “This is not something that can be left to the local communities,” Smith insists.

As part of its project, the Rotary Club of Calcutta made sure to allow for regular maintenance and periodic replacement of the filter cartridges, ensuring long-term effectiveness. On a two-week trip to Kolkata in 2024, Athulathmudali visited each of the villages to check on the state of the installations. Regular monitoring of water quality is crucial to the success of the project.

In another challenge facing the low-lying delta near Kolkata, sea-level rise and storm surges from intensified cyclones are increasing the salinity of groundwater. The area’s mangrove forests serve as a natural defense, and villagers are replanting them in places to act as barriers along with earthen embankments, demonstrating that the solutions to the region’s water woes must be multifaceted.

For now, the quality of life has improved in areas with the new water filters, including in Kayal’s village of Kankura. “For adults and children alike, there’s no greater blessing than clean water,” he says. “It is the biggest investment towards our future.”

This story originally appeared in the January 2026 issue of Rotary magazine.

related stories

Tó éí ííná át'é: Water is life

Engineer follows the science of water

Rotary 360: Clean water in Darién, Panama