Now proposals are on the table to mine in an area northwest of Ermelo, where the Vaal River originates. It is called the Spitzkop Greenfields Project and the prospective mining company is Xstrata, which owns several mines in the Mpumalanga highveld coal fields.
Professor Terence McCarthy of the school of geosciences at the University of the Witwatersrand has written to Xstrata's consultants, warning that if the project goes ahead, it is likely that within a decade the water quality in the upper Vaal will deteriorate to the point where it will no longer be fit for human consumption.
The Grootdraai Dam would then no longer be able to supply water for the Gauteng region.
"I believe that it is in the national interest that the project should not proceed," McCarthy says.
He explains in his letter that the proposed mining area encompasses a large portion of the headwaters of the Vaal River, and it is almost certain that the proposed mining will result in serious pollution of this river system.
"We know from past experience on the Olifants River in the Witbank area, where companies like Xstrata and AngloCoal are currently mining, that serious pollution of the river is unavoidable.
"In that case, the miners have managed to use the Witbank dams in conjunction with a controlled release policy to contain the pollution for the moment. This control is only temporary, however, and will be lost when the mines close.
"On the tributaries of the Wilge River such control is not possible, and serious pollution has resulted. The salt load in Loskop Dam is steadily rising, with serious ecological consequences," writes McCarthy.
Similar concerns have been expressed about prospective mining on the Drakensberg escarpment near Wakkerstroom in an area that contains the headstreams of four major rivers - the Vaal going west, and the Usuthu, Pongola and Tugela flowing to the Indian Ocean.
Delta Mining Consolidated has been granted permits to prospect there for torbanite, a form of coal that is rich in oil.
Fears have been expressed that the mining would affect the groundwater table and pollute the rivers.
Koos Pretorius, chairman of the Escarpment Environment Protection Group which has been established to fight ecologically destructive mining further north along the escarpment, told the meeting that there were 114 applications for mining in the region.
Noting the calamity this spells for the rivers and, ultimately, for the northern provinces' water supplies, Angus Burns, the co-ordinator of the Enkangala Grassland Project, a conservation group in the region, said: "There is more coal in less sensitive areas outside the escarpment region than we'll ever be able to exploit. Why then mine for it in ecologically precious areas that contain no more than 15 percent of our coal deposits?"
Acid mine drainage results from the exposure of coal and broken rock. Mines treat the water with lime to reduce the acidity. It is kept in reservoirs and released in a controlled manner into rivers when their levels are sufficient to dilute the remaining acidity.
The threat to fresh water supplies from mining is in addition to growing alarm at the leakage of sewage into rivers and underground water systems.
Concern about the water situation was echoed this week by Dr Morne du Plessis, the chief executive of the Worldwide Fund for Nature (WWF) in South Africa.
He said more than 98 percent of our freshwater supply was already accounted for, and that at current rates of supply and consumption, we'd run out of fresh water by 2025.
"Government, civil society and the private sector must work together to build a future in which healthy aquatic ecosystems underpin the sustainable development of South Africa and enhance the quality of life of all its people."
Lindiwe Hendricks, the minister of water affairs and forestry, has responded to reports about acid mine drainage, saying the mines were co-operating with the government.
This article was originally published on page 3 of The Sunday Independent on February 10, 2008