EE WAS CHANGING AN OUTSIDE LIGHT AT PIT CAR AND STEPPED ONTO A 20' WATER LINE TO CROSS TO THE OTHER SIDE. FOOT SLIPPED OFF PIPE. AREA AROUND THE PIT IS TYPICALLY WET AND CAUTION SHOULD BE USED WHENEVER AN EE HAS TO CROSS OVER ANY PIPE LINE. PROPER FOOTING AND SPEED SHOULD ALWAYS BE USED WHEN PERFORMING THIS TASK.