Download 8 Purification Posters
How is Tap Water Cleaned (214KB)
Rand Water draws water for purification (cleaning) from the Vaal Dam through an intake tower.
When raw water arrives at a purification station it passes through metal screens.
Coagulation and Flocculation (231KB)
The raw water enters the middle of a spiral flocculator where slaked lime is added. This is thoroughly mixed in the rapidly moving water.
The water flows slowly into large sedimentation tanks. The 'floc' then settles to the bottom of the tank to form 'sludge'.
When water leaves the sedimentation tank it has a pH of about 10.5, from the slaked lime that was added.
The pH of the water has now been corrected through carbonation, but it still contains some small living organisms and germs.
Even after the water has been filtered it still contains some germs. To kill these germs, chlorine gas is mixed with the water.
Water Supply (237KB)
The clean water is pumped through underground pipes to booster pumping stations. The chlorine is only effective for 6-8 hours so it is necessary to add chloramine.