The Brownhill Creek Catchment can be divided into two main zones - the Hills Zone (rural catchment) and the Plains Zone (urban catchment). The Hills Zone is underlain by fractured rock aquifers which contain good quality groundwater (salinities below 1000 mg/L) and have a strong interaction with surface water flows. Using only existing information, a water balance for this zone suggests there is significant potential for increased groundwater withdrawals (about 1000 ML/year). However, the local effects of any large increases in pumping on groundwater levels and environmental flows in streams needs to be further investigated by groundwater modelling and monitoring. The relationships between groundwater pumping, baseflow and the minimum streamflow required for environmental purposes are important questions to be resolved, not only for this catchment, but for the Mt Lofty Ranges as a whole. The Plains Zone overlies Quaternary alluvium and Tertiary marine sediments of the St Vincent Basin. The confined Tertiary limestone aquifer also contains good quality groundwater (salinity below 1500 mg/L), with very good potential for withdrawals as well as Aquifer Storage and Recovery applications, because of the high yields obtainable (up to 30 L/sec).