In many parts of the developing world, aid workers have often struggled to get people clean, disease-free drinking water. Surprisingly, it hasn't always been easy. For a while, aid workers helped people get clean water by digging wells. But by the time people got the water into their homes it was often still contaminated. The next step involved adding a tiny bit of chlorine, which keeps water free of germs for days. So aid workers started trying to get people to use chlorine. In Kenya today, you can buy little bottles of chlorine, made just for purifying water, for pennies. Problem solved? Unfortunately, surveys show that only a small percentage of people buy the chlorine, even though it's cheap and widely available.

So the next step to help rural areas get clean water involved putting chlorine right next to the spring or well. It's basically an upside-down bottle with a dispenser that releases chlorine into the containers people use to carry water. A tiny bit is enough for 20 liters of water. It's simple and it's free.

But it turns out that only 40 percent of people who have access to the dispensers actually use them. Some people don't like the taste; some people don't believe in it. The American aid workers sometimes don't use the dispensers either. One aid worker said, "Sometimes you're in a rush, or you're thinking about something else and you just don't do it. I've had malaria five times now. I have a bed net hanging above my bed, and I don't use it."

What's the real problem? The article zeroed in on one issue—human nature. In other words, people from Nairobi, Kenya to New York City often know what's right but we don't do it. Interestingly, the NPR blog that reported this story was titled "A Surprising Barrier to Clean Water: Human Nature."