What was found
NO WATER IN GALLEYS AND LAVS WHEN AIRBORNE BUT WORKS ON GROUND WHEN LANDED REMOVED AND REPLACED THE H2O SYSTEM UNDERLOADER CHECK VALVE, FOUND BAD. PRESSURIZED THE SYSTEM WITH 1 ENG IDLE, OPS CHECK GOOD. H2O AIR COMPRESSOR INOP. REMOVED AND REPLACED THE AIR COMPRESSOR REF AMM 38-15-01-404-029. POTABLE WATER SYSTEM PRESSURE OPERATING NORMAL AT THIS TIME. ROTABLE PARTS CHANGE WAS INDICATED - TT # 1122500 SN OFF 4895 IPC REFERENCE # 38-15-01-50.