Where do we get our water from?
The City of Cape Town receives the majority of its water from 6 major dams (99.6%) and several minor dams (0.4%) amongst other smaller sources.
(Did you know? A dam is the barrier e.g. wall, that creates the storage of water. The storage is called a reservoir. In common language we refer to the combined site as a dam).
|Major Dam||Storage Volume ML||% of Total Storage*||Ownership|
|Berg River Dam||130 010||14,47%||National Department of Water and Sanitation (DWS)|
|Voëlvlei||164 095||18,27%||National Department of Water and Sanitation (DWS)|
|Theewaterskloof||480 188||53.46%||National Department of Water and Sanitation (DWS)|
|Steenbras Upper||31 767||3,54%||City of Cape Town|
|Steenbras Lower||33 517||3,73%||City of Cape Town|
|Wemmershoek||58 644||6.53 %||City of Cape Town|
|TOTAL STORAGE||898 221||100%|
*Note the dams must also provide water to other users not just for drinking water supply e.g. Agriculture and maintaining environmental flows. Furthermore, Steenbras (Upper and Lower) are a peaking power hydroelectric pump storage scheme and provides water to the Rockview Dam for the Palmiet Pumped Storage Scheme, so the system needs to maintain some water for the operation of these electricity generating plants.
When reviewing the dam level dashboard, it is important to consider the size of the dam (reservoir) not just the percentage of fullness. For example, although Theewaterskloof Dam is currently at 18% (the lowest dam level), this still equates to 86,433ML which is more than double the full volume of Steenbras Upper or Lower and a greater volume than Wemmershoek Dam. (This does not mean we can abuse the water.)
More information about the Western Cape Water Supply System: http://resource.capetown.gov.za/documentcentre/Documents/Graphics%20and%20educational%20material/Water%20Services%20and%20Urban%20Water%20Cycle.pdf
Why does it make a difference who owns the dam?
Berg River, Theewaterskloof and Voëlvlei Dams are owned by the Department of Water and Sanitation (DWS), a National Government Institution. There are other various users of this water e.g. farmers and other municipal areas that have licenses from the National Department. The City of Cape Town is just one of many users of the water from these dams. Water from these dams is operated and regulated by the National Department through the Regional Office. Although Theewateskloof Dam is at 18% (which is a bigger volume than Steenbras Dam), not all this water is allocated to the City of Cape Town, there are many other users that must also share this volume of water.
Whereas the Steenbras Upper, Steenbras Lower, Wemmershoek and minor Dams are owned by the City of Cape Town, and therefore the City has direct control over how this water is used. Unfortunately the storage capacity of these dams is far smaller (13,8%) than those of the DWS dams (86.2%) , and therefore these are being used more conservatively.
This is important because, the City if Cape Town’s restrictions can’t be applied to the users of the DWS dams. Restrictions must be placed on these users by the DWS themselves. While the City’s demand currently exceeds supply, the other users may still be within the limits of their allocations or supply.
What about groundwater?
There are several aquifers within the City of Cape Town municipal area, including Atlantis, Cape Flats, and Table Mountain Group. Access to the groundwater in these aquifers is via springs and boreholes. A spring is where the water flows naturally to the surface of the ground, and a borehole is where the water is purposefully pumped to the surface of the ground.
The City does use groundwater on a small scale as part of the water supply scheme. However, groundwater while a good emergency backup, also has its limitations.
Aquifers are also refilled by rain, that percolates through the soil. Therefore the current low rainfall also results in the slow recovery of the aquifers. Pumping too much water out of the aquifers can result in salt water intrusion from the sea into the aquifers; this is irreversible. For example: fill a glass with water, add a straw and start drinking, the water level starts to drop. Now add several more straws and several people to drink of them, the rate the water drops increases rapidly. Unless someone keeps filling the glass with water, the glass will be emptied quickly. In the cape aquifers, without rain percolating into the soil the voids are filled with salt water from the sea. Therefore the volume of water being pumped out, whether for commercial or private use, must be monitored and regulated. The monitoring and regulation of groundwater is done by the National Department of Water and Sanitation (DWS). The City is currently in talks with DWS to increase the regulation of groundwater in Cape Town, in order to prevent the abuse and subsequent loss of the aquifers.
All boreholes must be registered with both the Department of Water and Sanitation and with the City of Cape Town.
The Watershed Project, raising awareness about water: