FRONTLINE/WORLD returns to its story on a device that uses the energy of children to pump drinking water throughout southern Africa and discovers what has happened to the promises of the PlayPump and its boosters in the five years since its inception.

FRONTLINE/World investigates one of its own stories, "The Play Pump," which promised to use a merry-go-round and the power of children to help meet the dire need for fresh water in southern Africa. After FRONTLINE/World first aired the story in 2005, major donors in the United States - and the U.S. government itself - launched a multimillion-dollar campaign to install the device in thousands of African schools and villages. Now, correspondent Amy Costello investigates what happened to those communities, as the promise of the PlayPump fell short and the device's biggest American boosters began to back away from a technology they had once championed. Also in this hour: A journey to the Amazon and the remote rainforests of Brazil, where several major American companies are on the hunt for ways to capture an increasingly valuable commodity - carbon - as the Obama administration considers new legislation that would force them to pay for their pollution.