Johannesburg is surrounded by Mine Dump Sand for many Square Kilometers. More gold has been mined around Johannesburg in the last 130 years than in the whole of previous human history. Many of these mines have been closed. But many of these mine dumps contain uranium and cyanide residues. These are permeating down with rainwater into deep abandoned mines and filling up tunnels. The danger is will permeate into the water table and eventually into the Vaal River. Johannesburg and surrounding towns get their water including domestic-use water from the Vaal dam.
Measures has to be taken to avoid heavy metal poisoning from the residual uranium, and chemical poisoning from residual cyanide.
Another dam that supplies water to the Witwatersrand is the Hartebeest Dam. Sewages spillages into the dam from sewage has resulted in the growth of areas of poisonous algae in parts of the lake of the Hartebees dam. Environmental activists have been active in attempting to get the organisations producing the sewage to take remedial action.
The conclusion is that environmental action is very necessary to maintain the health quality of water used by people around the Witwatersrand.