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 Play Pump fell short and the device’s biggest American boosters began to back away from a technology they had once championed. Also in this hour: Adam Davidson of NPR’s “Planet Money” team looks at a new idea in post-disaster relief being tried out in Haiti, and a profile of a painter who travels to the remote jungles of West Papua in search of the “clever bird.”