Sharing Smarter

Rivers can recover when neighbors cooperate. The Rhine is the best proof. After decades as one of Europe's filthiest rivers, the countries along it agreed to strict cleanup rules in the 1980s. By the late 1990s, salmon were swimming home to the lower river for the first time in decades, and in 2012 they reached Switzerland for the first time in over half a century.

Markets can help too. Australia's Murray-Darling Basin lets farmers buy and sell water rights, rewarding whoever wastes the least.