Numbers are one way to make the destruction of war legible: number of hostages, number of children killed, number of buildings destroyed, number of aid trucks that made it across the Egyptian border. For Marwan Bardawil, who lives in Gaza, the unit of peril he tracks is cubic meters per hour. Bardawil is a water engineer with the Palestinian Water Authority overseeing Gaza. And these days he is measuring, in cubic meters per hour, the quantity of water flowing through the pipes that, in prewar time, carried 10 percent of Gazans’ drinking water—pipes that are controlled by Israel. Right now, with other water sources dwindling, those pipes are Gaza’s lifeline. “The people are really in need of each drop of water,” he told me. For the past week, I’ve been checking in with Bardawil every day as he struggles to find clean sources of water. (You can hear our phone conversations on this week’s episode of Radio Atlantic). In the best of times, Bardawil’s job is difficult. Gaza sits between a desert and the Mediterranean …