The coupling Cu/Cu-P brazing, which is that most employed in domestic water supply pipes, has been investigated. Potentiostatic corrosion experiments were performed in domestic water under different conditions. It appears that the brazing has a better resistance than copper. The nature of the films formed at the sample surfaces was determined by various analysis techniques and the thicknesses were measured by ellipsometry. It was observed that it was the difference in composition of the films, formed at copper and brazing surfaces, which allowed the Cu-P brazing to become more noble than copper. The relatively thicker film formed on brazing, appears to contain mainly calcium carbonate and sulphate which grow epitaxially on calcium phosphate (hydroxyapatite or brishite). The corrosion resistance of the studied brazing was not only related to the galvanic coupling copper/brazing, but also depended on other parameters, mainly the water-flow velocity.