By Paul Polak Everybody in the world knows about big dams. They do irreparable damage to the environment and the  millions of people they displace, but we need to keep building a few of them to feed the nine billion people we expect will live on planet earth when its population stabilizes. Ten years ago, ten world experts both for and against big dams formed the World Commission on Dams and reached a stunning consensus on the path forward, which the World Bank promptly decided to ignore. But there has been no World Commission on Buckets and Sprinkling Cans, although some 50 million poor farmers in Asia…