B737 WATER SERVICING PANEL WAS INCORRECTLY CONFIGURED. WATER LEAKED DURING FLT AND COATED SIDE OF ACFT FUSELAGE WITH ICE.

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THE FLT ATTENDANTS NOTIFIED ME THAT THERE WAS NO WATER PRESSURE IN THE LAVATORIES FOR THEM TO WASH THEIR HANDS. I CALLED ON THE FLT INTERPHONE AND SPOKE TO THE PERSON ON THE HEADSET; CONTRACT GND CREW; AND ASKED THEM TO PLEASE CHK THE WATER SVCING PANEL TO VERIFY THAT THE WATER SVCING HOSE WAS DISCONNECTED AND THE RELATED SWITCHES CORRECTLY CONFIGURED. HE RPTED BACK TO ME THAT IT WAS. I THEN CALLED THE FLT ATTENDANTS AND ASKED THEM TO CHK THE LAVATORIES AGAIN FOR WATER PRESSURE. THE FLT ATTENDANTS RPTED BACK THAT IT WAS 'BETTER' AND THEY HAD WATER FLOW. I CONSIDERED THE MATTER CLOSED WITH THE WATER SYS FUNCTIONING CORRECTLY. WHEN WE ARRIVED AT OUR DEST (AN HR LATER); THE RAMP AGENT (A DIFFERENT PERSON) CAME UP TO THE FLT DECK AND TOLD US THAT THE WATER PANEL WAS NOT CONFIGURED CORRECTLY; ALL THE WATER HAD LEAKED OUT; AND THE SIDE OF THE ACFT WAS COATED IN A SHEET OF ICE. SOMETIME FROM SVCING TO ARR WE HAD DUMPED ALL OF OUR WATER DUE TO THE WATER SVCING PANEL BEING INCORRECTLY CONFIGURED. THIS IS ESPECIALLY DISCONCERTING BECAUSE I SPECIFICALLY ASKED THE GND CREW BACK IN ZZZ TO SPECIFICALLY VERIFY THIS SYS WAS CONFIGURED CORRECTLY. I WAS TOLD THAT IT WAS WHEN IN FACT IT WAS NOT. THE CREW ON THE RAMP NEEDS TO BE ABLE TO CORRECTLY SVC THE WATER SYS AND CONFIGURE THE WATER PANEL AFTER SVCING. WHEN SPECIFICALLY ASKED TO VERIFY THE CORRECT CONFIGN OF THE WATER SVCING PANEL THEY NEED TO RECOGNIZE WHAT IS CORRECT AND WHAT IS NOT. IF IT IS NOT CORRECTLY POSITIONED THEY NEED TO RECOGNIZE THE ERROR AND BE ABLE TO CONFIGURE CORRECTLY OR NOTIFY THE FLT DECK TO CONTACT MAINT. GND PUSHBACK CREW FAILED TO DETECT INCORRECT CONFIGN OF WATER SVCING PANEL. THIS RESULTED IN NO WATER PRESSURE; WATER LEAKING OUT AND FREEZING ON THE EXTERIOR OF THE ACFT.