Piotr Wolski has produced a tool to assess the current and projected state of the Western Cape Dams: The “Big Six Monitor”
The “Big Six Monitor” – http://cip.csag.uct.ac.za/monitoring/bigsix.html shows the amount of water in the major Western Cape Water Supply System (WCWSS) dams currently and in the recent past.
Additionally, it shows the storage in the dams projected for the period between now (i.e. day for which the most recent data for dam storage are available) and June 2018.
You can interactively define some parameters of the system that affect state of the dams, such as water use and yield of water resource augmentation schemes (i.e. desalination plants or groundwater wellfields) that are planned to be implemented in the near future, and thus explore their implications to availability of water.
This is a slightly revised version of (once-off) analyses presented here.