The Fittings Fail First Here

PEX took over this market’s construction era for good reasons, but the brass fittings joining it became the system’s weakest link. Virginia Tech research on brass dezincification documents how inexpensive high-zinc brass fittings in PEX systems made this corrosion a significant national problem, with the zinc leaching out of the alloy until the fitting turns porous and weeps.

The visible tell is a white powdery crust on the brass, and the invisible one is a whole house full of identical fittings from the same batch. Add crimp connections that were only ever as good as the tool and the hurry behind them, and you have the local failure map: not old pipe, but young connections finishing early.