As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF FROM CDG UNABLE TO GET WATER PRESSURE TO GALLEYS OR LAVS. DUMPED FUEL AND DIVERTED TO LHR. *S/D* CAUSE WAS DETERMINED TO BE THE QUANTITY/PRESELECT SWITCH (P/N: 42HY331448-3) NOT BEING IN THE OFF/RESET POSITION. THIS CAUSED THE PRESELECT OVERFLOW FILL VALVE TO REMAIN OPEN CAUSING PRESSURE TO BE VENTED OVERBOARD. THE CONDITION WAS CORRECTED BY RESETTING THE QUANTITY PRESELECT SWITCH.