Customer reported old supply line was leaking. Replaced supply line. Open arrival I noticed customer had large amounts of moisture surrounding toilet and behind toilet causing mold growth to occur behind wall on toilet. Inspected toilet to try and determine if moisture was coming from toilet not was not able to identify any leaks in toilet. Recommended to customer to keep an eye on toilet and see if moisture re- occurs. If problem continues then we may need to replace toilet. Also explained to customer that excess moisture could be a result of condensation build up from showering.