With the City of Cape Town seeing a continued reduction of water, it is beginning to seem more likely that the city could see its ‘Day Zero’ pushed well into the region’s rainy season.

This is because the City has remained conservative in some estimates, with the current ‘Day Zero’ of 15 July 2018 not necessarily a true representation of the when the City may actually run dry – as evidenced by the day being pushed back by more than four months since the end of January.

“Regardless of rainfall or water supply augmentation, Cape Town needs to continue striving to reduce average daily consumption to 450 million litres a day (MLD),” the City said in a statement on Thursday.

“This must be done not only to stretch our supplies as far as possible, but also because the National Department of Water and Sanitation has imposed a 45% restriction on the City’s water use for the current hydrological year (1 November 2017 – 31 October 2018).

“If we do not adhere to this restriction, there is a chance that the National Department may impose even more stringent restrictions on Cape Town in November 2018,” it said.

The City added that it was now in a position to exercise greater control on the consumption side with the implementation of Level 6B restrictions, the increasing roll-out of pressure management across the City and the installation of water management devices to limit the consumption of high water users.

“It is important to note that previously we did not pre-emptively assume the effects of any of these interventions on Day Zero projections, but rather fed them into the model as they occurred,” it said.

“In calculating Day Zero, we believed it would be irresponsible not to take a conservative approach which assumed the worst case scenario.

“Using a conservative projection meant that the date would shift out under more favourable conditions, but this was deemed less of a risk than assuming a less conservative approach, and then having the date move closer if conditions were less favourable,” the City said.

Rain

Of course, the one factor the City cannot fully predict is the rainfall expected this winter.

It therefore drafted three different scenarios for Day Zero, based on no rainfall, rainfall at 100% and rainfall at 85% of the total received in 2017.

These projections can be further adjusted to reflect different levels of consumption. The graphs below show projections for consumption of 450 MLD (the City’s target) and 600 MLD (where the City was tracking a few weeks ago).

“The impact of our augmentation programme was also considered, with the graphs indicating the impact of no yield from augmentation, and 80% yield (once again, we are projecting conservatively),” the City said.

The projections also assume that the agricultural users have complied with the restriction target of the National Department of Water and Sanitation, and that they will continue to do so for the remainder of this hydrological year.

The first graph shows how the Day Zero date has been calculated up to now, with no rainfall:

Scenario 1

Scenario 2

Scenario 3

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