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Cleaning Poop from Drinking Water

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Bangladesh -- a country just east of India on the Bay of Bengal -- is known for its lush, tropical environment and extensive river system. It’s capital, Dhaka, is the tenth largest city in the world and travel by boat and Rickshaw is a common way to get around town. While the waterways are an inviting lure to this populated city, water is also the source of many diseases, particularly in Dhaka’s crowded slums. Here, sewage can seep into low-pressure, old, leaky pipes that transport the town’s drinking water, exposing residents to harmful bacteria and viruses.

Drinking contaminated water can lead to diarrheal disease and sometimes even death. In fact, according to the World Health Organization, diarrhea is the second leading killer of children under five years of age worldwide, and it is often caused by contaminated water.

Dr. Stephen Luby, a professor of medicine at Stanford University and senior fellow at Stanford Woods Institute for the Environment, wanted to change that.

At the time, Luby was working at the U.S. Centers for Disease Control and Prevention in Bangladesh, and he was all too familiar with the number of people who were getting sick and dying from preventable waterborne diseases. In the developed world, big expensive water treatment plants clean drinking water. However, poorer countries, like Bangladesh, don’t have the resources to implement these treatment plants. Instead, residents have to clean their drinking water themselves using expensive or fragile filters, chlorine tablets or boiling the water. These types of strategies often prove difficult and cumbersome for residents.

“What that model asks, is to say ‘Let’s have the poorest people in the world each set up a water treatment plant in their home.’ That’s actually a big undertaking. And these are the folks who are already trying to figure out ‘How am I going to get enough money to pay rent and to feed my family?’” explains Luby.

Amy Pickering with a handpump
Amy Pickering, a research associate at the Woods Institute for the Environment at Stanford University, posing with a hand pump. Courtesy of Amy Pickering/ Stanford University

Luby enlisted the help of Amy Pickering, a research associate at Stanford Woods Institute for the Environment and in the department of civil and environmental engineering at Stanford University. Along with Jenna Davis, a professor in the department of civil and environmental engineering at Stanford University and at the Stanford Woods Institute for the Environment, they were hoping to come up with a solution to clean contaminated water that was much cheaper than traditional centralized water treatment plants, but that didn’t require users to do any extra work. They call their effort the Lotus Water Project.


Pickering went to Dhaka to investigate possible solutions. She observed that women in the slums in Dhaka were using communal hand pumps to collect water in containers and store for later.

"What we realized is that we needed a technology that could be compatible with these manual hand pumps that people are using to extract water from the systems," said Pickering.

They thought that if there was a device that attached to the hand pump that would clean the water as it was pumped out, then residents would have easy access to clean water. Learning that nothing like this already existed, the team realized they were going to have to develop something themselves. So Pickering packed a 70-pound hand pump in her suitcase and brought it back to Stanford.

Under the guidance of Luby and Davis, Pickering and a team of students at Stanford began developing a solution. They needed to create a device that would be cheap, easy to maintain and robust to hot temperatures and monsoons. It also couldn't rely on electricity since electricity can be hard to come by in Dhaka’s slums.

They decided to use liquid chlorine as the way to clean the water because it’s cheap and readily available in household bleach throughout Dhaka and in many places throughout the world.

But how were they going to inject the chlorine into the water without using electricity? They turned to a physics principle called the Venturi effect to accomplish this. The Venturi effect explains that when water is forced through a constricted pipe, like a funnel, the pressure of the water decreases. Pickering and her team created a system that uses the drop in water pressure caused by the Venturi effect to create a suction, which in turn sucks in chlorine stored in an attached tank. At the heart of the system is a funnel-like device that attaches to the outflow of the hand pump. They call the device "the Venturi" and they actually design and 3D print it themselves.

Venturi device
A funnel-like device attaches directly to the hand pump and is connected to a tank that holds chlorine. When the water starts flowing through the funnel, the drop in water pressure causes the chlorine from the attached tank to be sucked into the water stream, thereby cleaning the water.

They prototyped many different designs both in the lab and in the field in Dhaka. They tested for durability, leaks, ease of use and functionality which included testing water samples for chlorine and bacteria levels. They also interviewed and spoke with residents to understand what they liked and didn’t like about their system. They would then incorporate what they learned from user feedback and field testing by modifying their designs, often 3-D printing new devices throughout the night in their rented apartments in Bangladesh.

They now have proof of concept that their device can work in Dhaka, and they are currently looking at possible business models and talking with companies to try to begin implementing in the field.

“Right now, we’re in conversations with for-profit companies that might be interested in taking this technology and commercializing it, and we’re really excited about that. Because what we want to see is this technology being scaled up and distributed throughout the world,” says Pickering.

They estimate the device capital to cost $20 or less when produced at scale. The eventual goal is that their system will not only be used in Dhaka, but in other places in the developing world where contaminated water is often found at shared water points.


This video is part of our Engineering Is: Cleaning Poop from Drinking Water e-book. The e-book explores the science and engineering principles behind the Lotus Water project's device designed to purify drinking water in Dhaka, Bangladesh. The e-book includes videos, interactives and media making opportunities. You can find all of our e-books at kqed.org/ebooks.

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