The hydrogeology of a 68 000 km2 region of arid central Australia has been assessed and mapped at 1:500 000 scale using a GIS to interpret various spatial data sets and compile statistics of water bore information. This work forms a part of the Western Water Study, a collaborative venture between Federal, Territory and Aboriginal representative agencies, which has the objective of improving access to groundwater information for Aboriginal people on their land. The study area is underlain by Proterozoic basement (Arunta Block), pre-Mesozoic sedimentary basins (Amadeus and Ngalia Basins) and Cainozoic sediments. Based on the analyses of 850 water bores , the study area is mapped as seven different aquifer systems to cover regional variations in hydrogeology. Palaeodrainages act as a sink along which groundwater drains to associated internal discharge playas. Statistical groundwater data for these systems and the individual geological formations drilled provide a starting point for further groundwater assessment in other areas of central Australia that have similar geology. Only one aquifer system representing about 3% of the study area in Cainozoic sediments along a mountain range consistently provides low salinity < 1000 mg/L) potable groundwater, though potable water can occasionally be found elsewhere throughout the region. Large individual bore yields of over 20Us can be found in the pre- Mesozoic and Cainozoic systems while a lack of storage precludes sustained high yield production from bores in the Proterozoic.