Through an osmotic process we don’t pretend to understand, the mixing of fresh and salt water at the world’s river mouths produces enough energy to feed 20 percent of the world’s electricity demand, say Dutch scientists. Could we start running our gadgetry on salt power? Small projects in Norway and the Netherlands are testing out ways to harvest estuary energy, but membranes needed for the process are expensive and energy-intensive to produce, so salt-to-power technology is unlikely to be viable anytime soon. But pass the margaritas anyway.