Diana Nicholson holds water filters made from different materials.

It’s so simple – and it works. What looks like a large flowerpot is actually a water filter that removes E. coli and other harmful bacteria. Pour in contaminated water, and the clay filter makes it drinkable at a rate of one to three litres per hour.

“They’ve been extensively tested and shown to be very effective at removing bacteria from water and reducing cases of diarrhea,” says Diana Nicholson, a master’s student in engineering and international development.

The filter becomes more effective the more it’s used. As its pores become clogged with trapped bacteria, they prevent even more bacteria from passing through. The filter needs to be scrubbed occasionally to prevent the pores from becoming completely blocked. Although the filter is effective at removing bacteria, it can’t remove contaminants like arsenic, which occurs naturally in the water in countries such as Bangladesh, India and Nepal.

The filters are made of three ingredients: clay, rice hulls and water. The hulls are donated by a wild rice farmer in Manitoba. Nicholson mills the hulls down to less than a millimetre long. She then mixes the hulls with clay and water, forms the mixture into discs and heats them in a furnace.

“The rice actually burns out during the firing process, so it makes the clay porous for the water to flow through,” says Nicholson. “You want to have enough rice so the water will go through, but you don’t want to have too much, because if the pores are too big, then it won’t filter out the bacteria.” A silver nitrate coating on the filter acts as a disinfectant.

Nicholson is using a recipe from Resource Development International Cambodia that includes rice hulls and locally produced, unfired clay bricks. “We’re taking a waste product and turning it into a filter,” she says, adding that filters can also be made from coffee husks or sawdust, depending on what’s locally available. A filter system, including the flowerpot, costs about $10, and the filter itself lasts for about two years with daily use. She is looking at adding carbon fibres to the clay to strengthen the filters.

As a high school student, Nicholson became interested in water issues in developing countries. “What really inspired me is the fact that people still die from diarrhea today,” she says, adding that 88 per cent of cases are caused by unclean water and improper sanitation. “My brain can’t comprehend how that’s possible, how people can die from something that’s so easily preventable.”

The World Health Organization says up to five million cases of cholera occur annually, resulting in 100,000 to 120,000 deaths. Since cholera bacteria resemble E. coli, Nicholson says, “I’m hoping to be able to infer that, because the filters can remove E. coli, they should be able to physically remove cholera as well.” The water filters are easy to use and transport, making them ideal for parts of the world affected by flooding.