At rush hour, crowds pour from three expresses onto the 96th St. platform. When the local arrives, they press in, thinking only of home. But I see water, deep in the Catskills, flowing from the upper reservoir of the Power Authority at Blenheim-Gilboa down to the lower reservoir, turning huge turbines that power the subways during rush hours. I see too, a small pump slowly drawing water back to the upper reservoir off-peak. Five summers ago, my family, on vacation, listened as the Power Authority spokeswoman explained all this. We were the only ones in the pine-paneled room. Years later, I think of that small pump pumping slowly, steadily, every day off-peak and how motion draws on rest Brandywine 1/9/2000