B767 FLT CREW REPORTS WATER LEAKS IN CABIN THEN WATER SYSTEM FAILURE. FLT CREW RETURNS FOR OVERWEIGHT LANDING.

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ON TAXI OUT FLT ATTENDANTS IN AFT GALLEY NOTIFIED COCKPIT THAT AFT GALLEY WATER FAUCETS WERE TRICKLING WATER. CONTACTED MAINT AND THEY FELT THAT WATER WOULD STOP ONCE AIRBORNE AND PRESSURIZED. AFTER TKOF DURING CLBOUT; FLT ATTENDANTS RPTED WATER WAS FLOWING OUT OF FAUCETS AND WATER WAS ALSO ACCUMULATING ON GALLEY TECH CARTS WHICH REQUIRE ELECTRICITY. FLT ATTENDANTS COULD NOT DETERMINE THE SOURCE OF WATER ACCUMULATION. SHORTLY AFTER THIS; STILL CLBING TO CRUISE ALT; FLT ATTENDANTS RPTED THAT WATER HAD STOPPED FLOWING BUT THERE WAS NOW NO WATER AT ALL IN ANY LAVATORY OR GALLEY FAUCET. COFFEE MAKERS ALSO INDICATED NO WATER. POTABLE WATER GAUGE WAS FLUCTUATING BTWN 140 AND 80 GALS. CONTACTED MAINT CTL AND WAS ADVISED TO TRY TO CYCLE WATER SHUTOFF VALVE IN AFT GALLEY AREA. VALVE WAS CYCLED WITH NO CHANGE IN SITUATION. DECISION WAS MADE TO RETURN. SUPPLEMENTAL INFO FROM ACN 794255: AFTER APPROX 1 HR WHILE ENRTE TO ZZZZ THE ACFT HAD A MALFUNCTION OF THE POTABLE AND/OR LAVATORY WATER SYS. AFTER CONSULTATION WITH DISPATCH AND MAINT CTL; A RETURN TO ZZZ WAS ACCOMPLISHED; REQUIRING AN OVERWT LNDG. THE LNDG WAS MADE UNEVENTFULLY BY THE FO. WHILE TAXIING IN; ONE OF THE BRAKE TEMP INDICATORS REACHED LEVEL 7 AND THE 'BRAKE TEMP' LIGHT DISPLAYED ON THE FORWARD INST PANEL. AFTER BLOCK IN WE RAN THE PROC IN THE LIMITS SECTION OF THE FLT MANUAL. AFTER 15 MINS OF COOLING; THE HOT BRAKE COOLED TO 4 AND THE 'BRAKE TEMP' EXTINGUISHED; REQUIRING NO FURTHER ACTION PER THE PROC. MAINT WAS NOTIFIED.