A short 10 mins video explains 'Day Zero':
Early this year, the South African government announced that Day Zero was looming – a moment, after three years of unprecedented drought, when dam levels would be so low that taps would be turned off and people would have to fetch water at communal collection points.

After taking remedial measures, Capetonians managed to push back the date of Day Zero until next year. We visited the city to find out how the threat of an apocalyptic disaster has changed lives.
Link:https://www.theguardian.com/environm...ning-dry-video

There is only one reference to why the reservoirs are now 20% full and that it is the richer suburbs which have had to adjust the most - the townships may have 25% of the population, but use 4% of the water.