NEW DELHI – River systems help sustain lives and livelihoods. But, thanks to excessive damming and drastic overuse of their water resources, some rivers are drying up before reaching the sea. Nowhere is this truer than Asia. Building large dams has increasingly run into grassroots opposition in established democracies but has gained momentum in autocratic states, which often tout their benefits for combating droughts and water shortages. But as the Mekong River (Southeast Asia’s lifeline) illustrates, giant upstream dams can contribute to depletion and intensify parched conditions in downriver regions. The spate of dam building in Asian autocracies is exacerbating already fraught water security disputes. India and Japan demonstrate that dams and democracy normally don’t go well together. Whereas China continues to build giant dams, trumpeting them as symbols of its engineering prowess, the public pressures generated by the Japanese and Indian democracies act as a brake on ambitious water projects that displace many people or flood vast areas. For example, India’s plan to link up its major rivers through man-made canals remains in the realm of fantasy. But China’s similar program...