The more risk and responsibility agovernment hands over to the private sector in water andsanitation, the more powerful the incentives for betterperformance-but also the more demands on the government incommitment and preparation. So a government about to enterinto a long partnership for a water concession orbuild-operate-transfer arrangement - typically fortwenty-five to thirty years - needs to be sure that it doesnot overlook details that will later land it in messyrenegotiations. A lease is less demanding, but offerssmaller gains and will not fix such problems as chronicunder-investment. It will, however, give the government timeto prepare a longer-term option. In this Note, based ontoolkits recently published by the World Bank, the authorsets out the range of options for involving the privatesector in water and sanitation and reviews the lessons onwhat can make or break a private participation process.