A B767-300 Captain reports about the failure of Maintenance Control to properly address why water leaking from the First Class lavatories was able to leak past the forward cabin floor protective barrier and down into the main Electronics Equipment (E/E) compartment. Pilot believed the lack of any repair to the protective barrier rendered the aircraft un-airworthy.

Narrative

Upon arriving to the gate for our flight on a B767-300 aircraft; the Maintenance Technicians advised us that there was a problem with the two First Class lavatories. It seems that the both sink drains were plugged; and the deferral required that the water be turned off to the sink faucets. The initial attempt to shut off the water by using the shut-off valves failed. The valves would not fully shut off the water to the faucets. This required the Technicians to then disconnect the water lines and install caps on the supply lines. While installing the caps; a flood of water was introduced into the entry area by door # 1-L and across the aisle into the Forward Galley area. Cabin service was called to help dry the floors prior to boarding.The Technicians and I discussed the possible impact on the E/E (Electronic Equipment) compartment which is located just behind the cockpit and below the First Class lavatories and galley. The B767 floor in this area is designed as the primary barrier to water infiltration from the main cabin into the E/E compartment if a leak were to develop in either of the lavatories or the First Class Galley.Secondary curtains are also installed over most of the electronics as a backup if the primary barrier were to fail. They are; however; a secondary form of protection. An inspection of the E/E compartment was then performed by our AMTs; who found a puddle under the access door of approximately seven feet in diameter; as well as water dripping throughout the electronics bay. Discussions ensued with both the AMTs and Dispatch; and all agreed that the primary barrier had failed. Additionally; the area of the failure should be determined prior to any further flight in order to protect against any future leaks. The Maintenance Supervisor then requested that we enter a discrepancy into the aircraft history. Unfortunately; the aircraft had already been removed from the trip and the write-up was rejected.The discrepancy was then reported to Maintenance Control as a failure of the primary water barrier for protecting the E/E compartment as observed when the water leak occurred. The [logbook] sign-off for this discrepancy was to open the Main E/E compartment and let dry. As is evidenced by the log item; nothing was done to address the failure of the protective barrier for the E/E compartment. Since water and electronics don't mix well; this barrier failure and lack of repair seems to render this aircraft to be in an un-airworthy condition. The further operation of this aircraft; whether it be domestically or at night over the ocean; without repairing this discrepancy is far from the operational safety we and our passengers have come to expect from our airline.