This paper discusses the City of Calgary, Alberta, Canada's experience with a 1200 mm concrete water feedermain rupture in January 2004. This feedermain services a large pressure zone in the northeast sector of Calgary, servicing approximately 100,000 people. Within a few hours, pressure problems were reported throughout the pressure zone, and a major hospital was also reporting severe pressure problems. Fortunately, the water pressure was restored to the area within a few hours of the break. When the break was located, the extent of the damage was discovered and it was obvious that the concrete had severely deteriorated, and the pre-tensioned steel had virtually corroded away. An electromagnetic survey of the steel was done to determine if there were additional steel wire breaks in the feedermain and three additional locations were discovered to need repairs. Several engineering investigations were undertaken to determine the cause of the failure, including soil testing that indicated extremely high sulphate levels, which combined with the groundwater conditions led to the deterioration of the concrete, and the eventual corrosion of the steel. A hydrophone device was installed in the feedermain to "listen" for additional wires breaking. To the end of December 2004, 36 individual wire breaks have been heard. Test pits combined with soil results will be used to determine the limits of the replacement. Polyurethane-coated steel is being considered for the replacement at an estimated cost of $2.5 million. Includes 8 references, figures.