The fractured-rock groundwater systems of the folded Table Mountain Group (TMG) constitute a vast aquifer system extending from just north of Nieuwoudtville southwards to Cape Agulhas and eastwards to Port Elizabeth. The full volume of the aquifer rocks in this whole region comprises a staggering 100 000 km³.

The groundwater intersections or pathways in the TMG aquifer are commonly at depths of greater than 100m below ground. The depth and capacity of the system is evidenced by the several powerful hot-spring sources in the region with outflow at temperatures of up to 64° C. These temperatures are caused by the water being circulated to depths of at least 2000 m below ground level.

Cross-section of an artesian basin in the Cape Fold Mountains

The recharge to the Table Mountain Group Aquifer is believed to be in the range of 7% to 23% of Mean Annual Precipitation) (i.e. rainfall, snow and mist). On the higher mountain peaks of the TMG in the Western Cape the Mean Annual Precipitation exceeds 1000 mm and over the remaining TMG catchment it usually exceeds 600 mm. High snowfalls in the vicinity of the Hex and Ceres Valleys add considerably to the total recharge. The surface of the TMG aquifer is also conducive to infiltration, comprising a spongelike jointed and blocky rock with minimal soil cover. In the study area, the potential deep groundwater recharge is of the order 100 million cubic metres or more a year.

Groundwater associated with the TMG is characterized as being amongst the purest occurring in South Africa in terms of Electric Conductivity and Total Dissolved Solids. The quality of the water has been related to its source, namely the frontal systems which bring rain-bearing clouds from the Atlantic and Indian Oceans. However, the pH is as low as 5 which is very acidic and therefore corrosive. This pH range is common however, since streams fed from fynbos-dominated catchments in the Western Cape mountains typically have their pH between 4.5 and 6.5.

The TMG Aquifer largely coincides with the winter rainfall region of South Africa with reliable precipitation in the range of 600 to 1000 mm per annum. This is concentrated during the period June to September. Whether global climatic changes will lead to significant change in this winter rain and snowfall needs to be considered.