Old saris have a second use: They can protect people from a deadly bacteria in water.

For many of us here in the U.S., cholera is something we only know about from a book that we read in high school.

But for millions of people around the world, this disease is a very real threat to their health simply because they don't have access to clean drinking water.

So, what if there were an easy way to filter out cholera-causing bacteria from water?

That is exactly the question that marine microbiologist Rita Colwell pondered while she was on a research trip in Bangladesh.

She had been studying the bacterium that causes cholera, called Vibrio cholerae, for decades and had made a series of important discoveries about it with her colleagues. For example, they had learned the bacteria could survive in both fresh- and seawater and that it was the primary bacteria attached to copepods, microscopic crustaceans and plankton that live in water all over the world.

But up until then, their research had focused mostly on the bacteria and the environment where it was found — not on any practical solutions that might help people not get sick.

"It occurred to us, well, my goodness, in all the work we are doing, clearly we could do something for the village families who get cholera," Colwell says.

Cholera is a deadly diarrheal disease caused by the ingestion of contaminated food or water.

While this disease has been rare in the United States for over a century, it is still a serious problem throughout the developing world, including in Bangladesh, where access to clean drinking water can be difficult. In fact, according to the World Health Organization,between 1.3 to 4 million people get sick with cholera every year, and as many as 143,000 people die from it.  

In rural Bangladesh, where Colwell was working, cholera was a serious problem because women would scoop drinking surface water directly from canals, rivers, and lakes. There was no filtration, and there wasn’t enough fuel, like firewood, available for families to boil water every day.

Colwell and her colleagues realized that if they could devise a crude, inexpensive filter to strain the copepods (which the V. cholerae bacteria are attached to) from the water, maybe they could help people protect themselves from the disease.

They started by testing out T-shirt material, but that didn’t work. It was difficult to rinse, it didn’t dry, and a lot of debris in the water got through the weave in the fabric.

Then they tried sari cloth —the same cloth that women in India, Bangladesh, Sri Lanka, and Nepal have worn for thousands of years. It's also a cloth that women in rural Bangladesh already were using to prepare home-brewed drinks.

It worked.

The sari fabric, when it was folded four times over the urns used to gather water, created a mesh filter that was effective enough to remove 99% of the bacteria attached to the plankton copepods that cause the cholera.

Not only that, but the cloth could be reused over and over again, making it a very practical and inexpensive solution. That’s because the cloth is light and porous, Colwell explains. "Because it rains — with monsoons — every day [there], the sari cloth is designed to dry quickly. So, what is nice about it is that you can unfold it, rinse it off, and then hang it up. It dries and then you can re-use it."

Colwell and her colleagues taught villagers how to make their own sari filters in 65 rural Bangladeshi villages, and over three years, she says, "we were able to show a 50% reduction in cholera."

The team returned to the villages five years later and found that news of the filters had spread to other villages. As many as 75% of the population in these villages were using these filters.

And, Colwell says, they discovered something called the "herd effect" taking place — even if villagers weren’t filtering water themselves, fewer people were getting sick because fewer people were shedding the bacteria back into the water. "By virtue of all their neighbors staying healthy because they filtered," she explains, "they were not exposed to the larger numbers of bacteria themselves."

Of course, the filter isn't 100% effective at catching cholera-causing bacteria. Still, Colwell says there is power in this simple solution.

According to UNICEF, 663 million people do not have access to clean water around the world. Not only that, almost 2.4 billion people do not have access to adequate sanitation.  

There are a lot of high-tech solutions out there that try to address the problem of access to clean water, she says, and there are a lot of ways to work to combat the spread of cholera. But sometimes, it is the simple, inexpensive solutions — such as the sari filter — that can do a lot of good.

With more education about how the sari can be used, she says, it can make a difference for public health in regions where there isn’t access to clean water. Sari filters could even be useful in the aftermaths of large hurricanes, tornadoes, and other natural disasters all over the world, she adds.

Colwell and her colleagues hope to spread the word about sari filters to other places, such as Africa and other regions in Asia, where inexpensive solutions have the potential to make a big impact.