Stable isotopes in water (δ²H and δ¹⁸O) are important indicators of hydrological and ecological pattern and process. δ²H and δ¹⁸O of water are incorporated into geological and biological systems in a predictable manner and have been used extensively as tracers in hydrological, ecological and forensic studies. Physical processes result in spatial variation of δ²H, δ¹⁸O in water across the landscape (so-called “isoscapes”) and provide the basis for hydrological, ecological, archaeological and forensic studies. Southern Africa is a globally important meeting point for ocean and climate systems, biological diversity and human societies, yet there is little information on the spatial variability of δ²H and δ¹⁸O in water across this important region. Here we present the first ground water and tap water isoscapes for southern Africa. We compare and contrast these two water resources, and consider how well global models of precipitation isotopes capture isotopic variation across South Africa. Ground water and tap water samples were collected from across South Africa, analysed for δ²H and δ¹⁸O, and used to generate interpolated δ²H, δ¹⁸O and deuterium-excess (d = δ²H – 8*δ¹⁸O) isoscapes. We found coherent spatial structure in δ²H, δ¹⁸O and d of ground water and tap water that could be predicted by a geostatistical model based on simple environmental parameters (elevation, mean annual precipitation, precipitation minus potential evaporation, distance to coast and modeled isotope ratio of precipitation). This spatial structure resulted in considerable differences in isotopic composition of water in many of the major wildlife reserves in South Africa, indicating a good potential for wildlife forensics in this region. δ²H and δ¹⁸O of ground water, and to a lesser extent tap water, reflected the δ²H and δ¹⁸O of long-term weighted annual precipitation at the two GNIP stations in South Africa. However, large discrepancies between modelled isotopic composition of precipitation and our ground water and tap water isoscapes, particularly at higher elevations, highlighted uncertainty in the accuracy of modelled precipitation isoscapes for this region. Increased spatial sampling of precipitation, especially for high elevation regions, and temporal sampling of ground and tap water would considerably aid isotopic studies in this region.