Most of the water used in the city of Windhoek is sourced some 500 km away, in the Berg Aukas area of northwestern Namibia (right), while the Windhoek aquifer only supplies about 10% of the demand. The schists and amphibolites of the Kuiseb Formation underlying the city of Windhoek are poor aquifers, but can be used as storage facilities in the dry and high evaporation environment of the central Namibian highlands. The Kuiseb schist encompasses several lithologies, dominated by garnet-muscovite-chlorite-biotite schist, with a distinctive pervasive cleavage, which makes the underlying rocks permeable to percolating water and fluids from the surface into the aquifer. Faulting also plays a significant role by increasing the fracture density of the fissile schist, and providing links between the surface and the aquifer below. Thus, close monitoring of all sewage pipes, filling stations, dump sites, including cemeteries, on a GIS-based model is essential to protect the aquifer from pollution.