Goats and Soda

How Salt + Car Battery = Clean Water


A woman in Yatta, Kenya, explains how to make clean water using a car battery and just the right mixture of salt and water.
Jane Mauser, Courtesy of MSR
A woman in Yatta, Kenya, explains how to make clean water using a car battery and just the right mixture of salt and water.

It's easy to take clean, safe water for granted. It just flow out of taps continuously — even in drought-ridden California.

But for hundreds of millions of people around the world clean water is a luxury. In many places, even patients in hospitals and kids at school don't have water that's safe to drink.

Now, an unlikely partnership of an outdoor equipment manufacturer and a global health NGO is trying to change that.

They've engineered a clever device that can make chlorine from just water, salt and a car battery. It's called the SE200 Community Chlorine Maker, and it uses technology developed by the military for water purification in remote areas.

Chlorine is a common way to disinfect water because it kills many bacteria and viruses. The problem is, though, chlorine isn't always easy to obtain. And it's hard to know how much to use.

Last week ago, I got a chance to see the SE200 in action, at a world development conference in the District of Columbia.

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The device is a small plastic canister that attaches to a battery with what look like miniature jumper cables. Using a special "brine bottle," you add salt and water in amounts indicated by lines. Mix it up, and add the salt solution to the SE200. With the push of a button, the canister illuminates, and the solution begins to bubble.

What looks like boiling water is actually a chemical reaction, called electrolysis, says Jesse Schubert, of the NGO PATH. The electricity from the battery causes the salt (i.e., sodium chloride) to break apart into sodium and chlorine ions. These elements then recombine into bleach, or sodium hypochlorite.

"There are other chlorine generators out there," Schubert says. But they can be expensive and difficult to use. "The innovation [of the SE200] is that the unique circuitry does calculations and always makes the right chlorine concentration," he says. One teaspoon of chlorine solution from the SE200 can treat five gallons of water.

Back in the early 2000s, the Defense Advanced Research Projects Agency, or DARPA, spent $6 million developing a pen-sized water purification system. Then PATH teamed up with Mountain Safety Research to turn the military technology into a product communities in developing countries could use.

Over the past seven years, MSR and PATH have field tested the SE200 in more than 10 countries, including Kenya, Ghana, India and Haiti. The companies released the device commercially last month.

The SE200 can provide clean water for schools, health centers and water vendors. Each device costs about $200. But it can treat enough water for 200 people for about five years, MSR says.

There are other devices available for disinfecting water in a single household and options for getting clean water to entire cities. But few devices are available for places in between the two sizes. That's the gap the SE200 is supposed to fill, says MSR's Laura McLaughlin.

At first, NGOs will distribute the water purifiers. But, the two companies want to eventually sell it directly to users.

And that's where the biggest challenge will be, says Mark Sobsey, an environmental scientist at the University of North Carolina. People using the chlorine maker will have "varying levels of skills, experience and understanding of water treatment and dosing chlorine," he wrote in an email. That means they can make mistakes.

To try to address this concern, McLaughlin and Schubert say, each kit comes with test strips to ensure the concentration of chlorine is right every time. Smiley faces indicate the ideal range. And the instructions for the SE200 are pictorial.

But the device can't disinfect all types of contaminated water. If the water is turbid, pretreatment with another process, such as filtration, should happen before adding chlorine — otherwise, the water might not be safe for drinking.

And there's always the issue of maintenance and repairs, Sobsey says. What happens if the device breaks? Who will fix it?

Despite these questions, Dr. Kellogg Schwab, thinks the SE200 is a great idea. He's the director of the Johns Hopkins Global Water Program, and he has been working with MSR to evaluate the SE200. He likes that the team has been giving thought to the whole supply chain. Instead of just giving out a device, he says, they're training operators and encouraging entrepreneurship.

But "when it comes to water, there are no silver bullets," says MSR's McLaughlin. "Many solutions are needed."

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