An underground municipal drinking water system, installed in 1927, comprised of a reservoir and discharge tunnel, feeding into a 48 inch cast iron piping system, operated for almost 50 years without issue. In 1973 the tunnel was inspected using commercial divers due to indications of leakage observed at grade. The inspection revealed some deficiencies in the tunnel portion of the system that were deemed to be minor, with measures to contain the leakage at the surface implemented. In late 2017, indications of a second, more significant leak was observed in the location of the cast iron pipe. A remotely operated vehicle (ROV) inspection of the pipe revealed a surprising reason as to the mechanism responsible for the leakage.