When THE CITY learned on the Friday before Labor Day that water tests at Manhattan’s Jacob Riis public housing complex detected arsenic and called City Hall for comment, Mayor Eric Adams showed up there within hours, distributing bottled water. Further testing showed no traces of arsenic — but as THE CITY revealed, those later tests were done only after taps had been flushed out for hours. After our reporting, the matter was investigated by NYCHA’s federal monitor.