INTRODUCTION How can you do the most good? Until 1989, Trevor Field was a typical middle-aged South African man who had lived a fairly normal life. He enjoyed fresh steaks, cold beer, and fishing with his friends. Working in advertising for magazines like TopCar and Penthouse , he had never thought seriously about using his skills for the greater good. When he discovered the PlayPump, however, everything changed. That year, Field and his father-in-law, a farmer, visited an agricultural fair in Pretoria. There, he met a water engineer named Ronnie Stuiver who was demonstrating a model for a new type of water pump. The demonstration reminded Field of a fishing trip he''d taken years before, during which he had watched the women of a rural village wait for hours next to a windmill-powered water pump. There had been no wind that day, but the women, who had trekked for miles, still needed to bring water back to their homes.

So they simply sat and waited for the water to flow. Field had been struck by how unfair this was. There simply must be a better way to do this , he thought. Now he was witnessing a potential solution. Stuiver''s invention seemed brilliant. Instead of the typical hand pump or windmill pump found in many villages in poor countries, Stuiver''s pump doubled as a playground merry-go-round. Children would play on the merry-go-round, which, as it spun, would pump clean water from deep underground up to a storage tank. No longer would the women of the village need to walk miles to draw water using a hand pump or wait in line at a windmill-powered pump on a still day.

The PlayPump, as it was called, utilized the power of playing children to provide a sustainable water supply for the community. "African [kids] have almost nothing--not even books in school let alone playground equipment--and access to water is a huge problem," Field later told me. "I thought it was just the best idea I''ve ever seen." Field bought the patent from Stuiver and worked in his spare time over the next five years to improve the design. Using his experience in advertising, Field came up with the idea of placing billboard advertisements on the sides of the water tank as a way to generate revenue to pay for pump maintenance. In 1995, he secured his first sponsor, Colgate Palmolive; installed the first PlayPump; and quit his job in order to focus full-time on the project, now a registered charity called PlayPumps International. Progress was slow at first, but he persevered, paying for several pumps with his own money. At the same time, he developed connections with corporations and government bodies across South Africa to pay for more pumps.

By the turn of the millennium, he had installed fifty pumps across the country. His first major breakthrough came in 2000 when, out of three thousand applicants, he won a World Bank Development Marketplace Award, given to "innovative, early-stage development projects that are scalable and/or replicable, while also having high potential for development impact." That award attracted funding and attention, which culminated in a site visit from Steve Case, CEO of AOL, and his wife, Jean. "They thought the PlayPump was incredible," Field said. "As soon as they saw it in action, they were sold." In 2005, the Cases agreed to fund the project and worked with Field to set up an American arm of PlayPumps International. Their aim was to roll out thousands of new PlayPumps across Africa. The PlayPump became the center of a massive marketing campaign.

Steve Case used his expertise from running AOL to pioneer new forms of online fund-raising. The One Foundation, a British fund-raising charity, launched a bottled water brand called One Water and donated the profits to PlayPumps International. It was a huge success and became the official bottled water of the Live 8 concerts and the Make Poverty History campaign. The PlayPump became the darling of the international media, who leaped at the opportunity to pun, with headlines like PUMPING WATER IS CHILD''S PLAY and THE MAGIC ROUNDABOUT. In an article for Time in 2006, Bill Clinton called the PlayPump a "wonderful innovation." Celebrities, too, jumped on the bandwagon. Jay-Z raised tens of thousands of dollars through his "The Diary of Jay-Z: Water for Life" concert tour. Soon after, PlayPumps International secured its biggest win: a $16.

4 million grant awarded by then First Lady Laura Bush, launching a campaign designed to raise $60 million to fund four thousand PlayPumps across Africa by 2010. By 2007, the PlayPump was the hottest thing in international development, and Trevor Field was at the center of it all--a rock star of the charity world. "It has just gone berserk! . . . When I first looked at this water pump . . .

I could never imagine that this is something that could possibly change the world," Field said in 2008, reflecting on PlayPump International''s startling success. "It really rocks me to know we''re making a difference to a lot of people who are nowhere near as privileged as I am or my family is." By 2009, his charity had installed eighteen hundred PlayPumps across South Africa, Mozambique, Swaziland, and Zambia. Then things went sour. Two damning reports were released, one by UNICEF and one by the Swiss Resource Centre and Consultancies for Development (SKAT). It turned out that, despite the hype and the awards and the millions of dollars spent, no one had really considered the practicalities of the PlayPump. Most playground merry-go-rounds spin freely once they''ve gained sufficient momentum--that''s what makes them fun. But in order to pump water, PlayPumps need constant force, and children playing on them would quickly get exhausted.

According to the UNICEF report, children sometimes fell off and broke limbs, and some vomited from the spinning. In one village, local children were paid to "play" on the pump. Much of the time, women of the village ended up pushing the merry-go-round themselves--a task they found tiring, undignified, and demeaning. What''s more, no one had asked the local communities if they wanted a PlayPump in the first place. When the investigators from SKAT asked the community what they thought about the new PlayPump, many said they preferred the hand pumps that were previously installed. With less effort, a Zimbabwe Bush hand pump of the same cylinder size as a PlayPump provided thirteen hundred liters of water per hour--five times the amount of the PlayPump. A woman in Mozambique said, "From five A.M.

, we are in the fields, working for six hours. Then we come to this pump and have to turn it. From this, your arms start to hurt. The old hand pump was much easier." One reporter estimated that, in order to provide a typical village''s water needs, the merry-go-round would have to spin for twenty-seven hours per day. Even when communities welcomed the pumps, they didn''t do so for long. The pumps often broke down within months, but unlike the Zimbabwe Bush Pump, the mechanics of the pump were encased in a metal shell and could not be repaired by the community. The locals were supposed to receive a phone number to call for maintenance, but most communities never received one, and those who did never got anyone on the phone.

The billboards on the storage tanks lay bare: the rural communities were too poor for companies to be interested in paying for advertising. The PlayPump was inferior in almost every way to the unsexy but functional hand pumps it competed with. Yet, at $14,000 per unit, it cost four times as much. Soon, the media turned on its golden child. PBS ran a documentary exposing the PlayPump''s many shortcomings. (One thing that didn''t change was the media''s love of puns: the documentary was called Southern Africa: Troubled Water ; The Guardian repeatedly referred to the PlayPump as "money down the drain.") In an admirable response to this criticism, the US arm of PlayPumps International shut down and its sponsor, the Case Foundation, publicly acknowledged that the program had been a failure. Yet, despite its fall from grace, the PlayPump lives on.

Under the name of Roundabout Water Solutions, Field''s nonprofit continues to install the same model of PlayPumps across South Africa, funded by corporations like Ford Motor Company and Colgate Palmolive. *   *   * Most people want to make a difference in their lives and, if you''re reading this book, you''re probably no exception. As Trevor Field''s story illustrates, however, good intentions can all too easily lead to bad outcomes. The challenge for us is this: How can we ensure that, when we try to help others, we do so as effectively as possible? How can we ensure that we avoid accidentally causing harm, and succeed in having the greatest positive impact we can? This book tries to help answer these questions. I believe that by combining the heart and the head--by applying data and reason to altruistic acts--we can turn our good intentions into astonishingly good outcomes. To illustrate, let''s look at a story with a very different ending from the one you just read about. *   *   * In 2007, at the peak of the PlayPump''s popularity, Michael Kremer and Rachel Glennerster launched an organization of their own, the culmination of decades of research into how to improve the lives of the poorest people in the world. Glennerster had studied economics at the University of Oxford, graduating in 1988.

She was interested in learning about poverty relief, so she decided to live in a developing country and spent a summer in Kenya. She spoke to people working in development, many of whom were deeply disillusioned. When she asked why, they told her to look at some of the ways development projects had back.