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Difference Maker

People Making a Difference: Bob Hildreth and Lisa Ballantine

These two innovators, working independently, provide cheap, effective filters that make polluted water potable.

By Moises Velasquez-Manoff /Staff writer of The Christian Science Monitor / June 15, 2009

Bob Hildreth (shown here at right) and Lisa Ballantine (in the photo below) try to get low-cost water filters that use sand and porous clay, respectively, into homes in the Dominican Republic.

Moises Velasquez-Manoff

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Puerto Plata, Dominican Republic

In 1991, Bob Hildreth drilled a well for his new home here. Not long after, people lined up at the spigot alongside his house. Potable water, he’d discovered, was in short supply.

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Eighteen years later – the longest time this former US Army aviator has spent in any one place – Mr. Hildreth devotes half his time to his jewelry business, Joyería las Americas, and the other half getting durable, low-tech water filters into the island's barrios.

Worldwide, at least 1.1 billion people don't have access to safe drinking water, according to the World Health Organization, and 2.4 billion lack basic sanitation. Some 1.8 million people die each year from diarrhea, which has been tied to unsafe drinking water – the majority of them children in developing countries.

Given that these losses are preventable, potable water doesn't seem to get the attention it deserves, says Mark Sobsey, professor of environmental sciences at the University of North Carolina at Chapel Hill. "Priorities are higher for other development activities than this," he says. "Sanitation, especially, is not very sexy."

Even piped-in water isn't necessarily safe, Hildreth says. In the developed world, constant water pressure keeps whatever's lurking outside the pipes at bay. In the developing world, however, where power outages are common, water pressure drops and at times even reverses, sucking in raw sewage that's often outside. When the system begins pumping again, it's delivering contaminated water.

"Point-of-use water treatment needs to be adopted by all the developing countries in the world," Hildreth says.

Funded principally by Rotary clubs, his organization – Project las Americas – has delivered 19,000 BioSand filters. One $50 filter cleans 120 gallons of water daily and lasts for decades. In studies, Dr. Sobsey has found that BioSand filters can reduce diarrhea by 47 percent. "You're almost certainly reducing mortality," he says.

Developed in the 1990s by Dr. David Manz, then at the University of Calgary in Alberta, BioSand filters use sand and the bacteria that grow on it to filter water. Users pour water through a diffuser into a gently tapering, belly-high container. (A traditional container made from cement weighs 250 lbs., but a new plastic container weighs just 10 lbs.)

Water passes through 20 inches of sand that comes directly from a quarry. The sand's tiny cracks and chambers filter out microbes. A layer of "good" bacteria forms at the sand's surface. This living film feeds on and removes viruses, bacteria, and parasites. "The technology is so robust that you can screw it up, and it will still keep functioning," Hildreth says.

Two hours inland, in the town of Jarabacoa (pop. 70,000), Lisa Ballantine works on the same problem using a slightly different tool: a ceramic pot filter. Smaller and lighter than the BioSand filter, hers fits into a five-gallon bucket. Pour water into the U-shaped receptacle, and it percolates through porous clay at a rate of two to three quarts per hour. Filters cost $30 to sponsor; Dominicans can buy them directly for $25. "The thing I like about [the] water [problem] is that we can solve it," she says.