The faucet at a public washroom I visited appeared quite ordinary. I turned the knob both ways, but nothing happened. I moved my hands under the spout half expecting a sensor to activate it. Still nothing.   Somewhat embarrassed, I looked around. The guy next to me seemed to know a thing or two about tricky faucets. He noticed my predicament and pointed below the basin counter. “Step on that thing,” he said.   I looked down—and lo!—there was indeed a metal foot lever. I stepp