Cape Town – The City of Cape Town has repeated its call to locals to continue to save drinking water, even though Day Zero has been pushed back again – this time from July 9 to July 15.
"People must continue to save, reduce their consumption," Deputy Mayor Ian Neilson told News24 on Monday.
"We can't afford to relax the water-saving efforts."
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Day Zero is a term used to describe the day that average dam levels reach 13.5%, and when an alternative water distribution plan is declared to make available water last through the rainy season.
The calculation of Day Zero is based on the previous week's daily consumption.
The last consumption figures available, from March 2, were 516Ml/day – still above the target of 450Ml a day, which is needed to completely avoid Day Zero.
The last average dam storage level was posted on March 2, and was at 23.8%.
Three possible scenarios
The City's water augmentation projects were at 64% completion.
The City's Department of Water and Sanitation has calculated three possible scenarios, based on: rainfall, consumption, dam draw-down and evaporation.
In the first, if there is no rainfall and demand drops to 540Ml per day, average dam levels are expected to drop to 13.5% and Day Zero plans will be triggered in mid-July.
This means that there will be a city-wide throttling of drinking water, except in informal settlements and parts of the CBD, which entails people fetching a daily ration of 25 litres of water from 187 points of distribution.
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It is not clear how long this operation will last, but the police and the SA National Defence Force are ready to implement the safety and security aspects. Dry runs have been conducted.
In the second scenario, if there is 100% of the winter rain that fell in 2017, and the water augmentation plans reach 80% completion, and consumption drops to the 450Ml per day target, average dam levels are expected to peak to around 37% by November and the 13.5% trigger point will be avoided.
At 600Ml consumption, dam levels should peak to 32.5% by November.
In the third scenario, dam levels should peak at 33% by November, but will then stop dropping again, if the target of 450Ml is reached.
This is if there is 85% of the winter rainfall of 2017, and 80% augmentation. With those conditions, at the higher consumption of 600Ml per day, dams should peak at an average 27% full by November and then start dipping again, into summer.
The charts plot a steady decline in water consumption into 2019 again.
Level 6B water restrictions, which limits the use of drinking water to 50 litres per person per day, became a local by-law in February.
Other measures taken, besides reducing consumption, was the Groenland transfer of water from farmers' private dams, and adjustments to water pressure to prevent waste.
The City's three small-scale emergency desalination plants will add approximately 16 million litres of water per day into the system by May 2018, and the three groundwater extraction projects will supply almost 150 million litres of water per day to the city at their peak.
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