Modern-day Ghana, like most African countries, is a European invention.

In September, when we last heard from adventuring educator and three-time Guinness World Record holder Dan Buettner, he had just provided us with an eight-part crash course on the ins and outs of the Galápagos Islands. Since then, his research on aging has appeared as a cover story in National Geographic and his work continues in Africa this year under the name of Blue Zones. Here's his latest report:

hile malaria may kill more kids in Ghana than anything else, the second biggest killer is so foul and distasteful that people don't even want to talk about it.

Our team has traveled 200 miles north of Accra to the country's second largest city, Kumasi. Kumasi is the capital of the Ashanti region. Accra was once dominated by the Ga people. Modern-day Ghana, like most countries in Africa, is a European invention. Historically, Africa was divided by tribes that lived within shifting borders. Today, the tribes still persist (there are over 1,000 different languages spoken here and five main ethnic groups); their land has been carved up just in the last century by colonies from England, France and Portugal.

The ride to Kumasi was harrowing. Having set a Guinness World Record for biking across Africa, I'm no stranger to the conditions here. But things seemed harsher today. Tin-roofed slums lined the road as we crept out of Accra in bumper-to-bumper traffic. Huge tufts of grey diesel exhaust blew out of tailpipes, clouding the already dirty air. At each stop, dozens of people would come to our car selling everything from plantains to phone cards and bubble gum to couches. I normally ignore vendors, but a cute little kid wearing a buzz cut, blue shorts and a mango-colored shirt stood out. He was selling clear plastic bags of chilled water from a huge basin balanced on his head.

"Why aren't you in school?" I asked.

"I've already been to school, sir," he replied politely. I looked at my watch. It was 3 p.m. Indeed, over 80 percent of Ghanaian kids go to school.

Untreated water can be deadly for African kids.

"What's your name?" I asked.

"Kofi, sir. It means I was born on a Friday."

I asked him where he got the water.

"From the tap in my village. I cooled them down in my auntie's refrigerator."

The water looked cool and clear, but I knew it could be deadly – maybe not to me, but to lots of kids like Kofi.

Untreated water often causes diarrhea and here – that kills kids. In Ghana, it causes the death of tens of thousands of children each year, more than anything besides malaria. More often than not, you get it from drinking water or eating foods contaminated with other people's poop.

A variety of microbes cause diarrhea: A virus (which causes 70 percent of the cases); cholera and typhoid fever (caused by a bacteria); dysentery (caused by amoebas); and giardia (caused by a parasite).

Most of the time, the diarrhea itself doesn't kill kids. At first, it's just an annoyance to have to run to the bathroom so often. But over days and weeks, as a child loses fluid from loose stools, he becomes dehydrated. His eyes sink into his head, his skin loses flexibility and he loses weight.

The end often comes from heart or kidney failure. Diarrhea is a foul sickness not only because of the mess it makes, but mostly because it is so easily treated. If a child is given regular drinks of a solution made from a half teaspoon of salt and six teaspoons of sugar mixed in a liter of water, he could be saved.

The diseases themselves could be reduced with better sanitation. Somehow here, sewage mingles too easily with drinking water (like in those bags on Kofi's head). Kids don't make it a habit to wash their hands with soap, and flies – which breed on disease-laden feces and then fly on food – are all too abundant. In America, we've adopted sanitation practices that eliminated all of these diseases but, as little as a hundred years ago, more people died from the diseases that cause diarrhea than they did from cancer.

Dan Buettner (visit his Blue Zones site).

The secret to longevity isn't complex or expensive. And here in Africa, there's a simple but powerful solution for saving millions of lives; it contains sugar, salt and water, and perhaps just a little more education.

Now, if you'll excuse me, I'm going to go wash my hands.