The invention is a precipitation sensor adapted to detect water upon an automotive glass and a method for its use. The precipitation sensor includes an optical emitter and a first mirror surface in optical communication with the optical emitter. The first mirror surface is adapted to reflect and collimate light emission from the optical emitter. The precipitation sensor also includes an optical receiver and a second mirror surface in optical communication with the optical receiver. The second mirror surface is adapted to focus collimated light upon the optical receiver. The precipitation sensor further includes an intermediate reflector in optical communication with the first mirror surface and with the second mirror surface.