During the last 33 years a great deal of geological work has been done in the elucidation of the mode of occurrence of underground water in all parts of the State; and this work. must be continued in a systematic way, in the interests of the public generally and of individual farmers, horticulturalists and pastoralists, as an essential part of the application of geological science to the needs of development. In this report the principles governing the storage of underground water are expounded in some detail, with many explanatory maps and diagrams. In addition, there is a full discussion of the way in which the composition of the salts dissolved in water is recorded, and also of the significance of salinity in the utilization of water, whether for human consumption, for watering stock, for irrigation, for industrial purposes generally, and for engineering use. The general features of the artesian basins of South Australia are described, and also the factors that determine the occurrence of groundwater supplies in parts of the State over which the artesian basins do not extend.