Water softening for municipal water supplies is not widely practiced in Australia and as such the technology involved is not widely known. This report investigates the current practice of municipal water softening. Methods of softening are considered and their relative merits examined. Attention is focused on the lime soda softening process as it remains the most widely used softening process for municipal water treatment. The chemistry of the carbonic acid system is also examined as it plays a dominant role in the lime soda softening process. Water softening for municipal water supply is currently carried out at the MuswelIbrook Water Treatment Plant. The design and operation of this plant is examined and options for improving and uprating the plant throughput are considered.