The rapidly growing populations of Cape Town and surrounding towns are putting big strain on the Western Cape’s water supply, water affairs warned on Monday.
The margin between available water and that used was about 8% (45 000 000m³) of safe supply, the department said in a statement, issued following the release of its latest water reconciliation strategy for the region.
According to projections contained in the report – which covers the six-month period up to March this year – this margin could be “fully utilised” within the next six to eight years.
“Population growth and the subsequent growth in the economy have been identified as major factors that are placing exponential strain on the water available for users of the Western Cape Water Supply System (WCWSS).”
The department said users included the City of Cape Town, as well as the municipalities of Stellenbosch, Drakenstein, Swartland and Saldanha, together with agricultural users.
“At present, the system can safely provide 556 000 000m³ a year. The 2010 water requirement on the system was already 511 000 000m³, of which 32% was used by the irrigation farmers and 68% by the urban dwellers supplied by the system.
“According to projections, the remaining 45 000 000m³ will be fully utilised anywhere between 2017 and 2019, depending on the growth in the area and the city’s… further successful implementation of its water conservation and water demand management programme.”
The department called on Cape Town residents to use water more sparingly.
“Without the support of the residents, the City of Cape Town would not have secure water resources,” it said.
Building more big dams was not feasible.
“According to the study, only a few surface water development options are available for augmenting water supply to the City of Cape Town and surrounding towns.”
However, the department was exploring alternative strategies to ensure sufficient water was available for future use.
These included “planning on going out on tender for a feasibility study of a large-scale sea water desalination plant” within the next month.
“The study will determine the most appropriate location and size for such a plant,” the department said.
The city also planned to do a feasibility study into the large-scale re-use of water, which would start within the next few months.
“[Other] investigations by the city, into the potential for large-scale ground water development and utilising the Table Mountain Group (TMG) aquifer as a sustainable water resource, are also underway.
“A decision on the implementation of a pilot wellfield development in the TMG will be taken by the city in the next couple of months.”
The department was also looking at two surface water options.
One involved pumping winter rainfall run-off water from the Berg River into the Voelvlei Dam; the other, diverting water from the Dwars River in Michell’s Pass, near Ceres, into the same dam.
The department said the eradication of invasive alien plants along the Western Cape’s river courses was becoming “increasingly urgent”.
“Each property owner along the rivers feeding into our dams and below the dams must begin to take responsibility for ensuring that their properties are clear of these water-thirsty plants.”
While augmentation of the WCWSS was receiving high-level attention, it was important to realise that all such interventions would take “many years” to deliver.
“The efficient use of the current supplies, including the curbing of water wastage and water losses, is of critical importance.
“All water-users in the system are called upon to use their water judiciously in support of the city’s water conservation programme,” the department said.
In December last year, water affairs’ Western Cape chief director, Rashid Khan, told Sapa that Cape Town would need to review its water-use strategy due to the “quite large numbers of people coming in” to the metropole and surrounding areas.
He said at the time that assumptions made by Cape Town’s water planners in 2007 were “now being overtaken by some serious developments, that is [population] growth”.
Khan also noted that the effects of climate change, if severe, could bring forward the construction of augmentation projects.
In this regard, climate forecasts for the next few decades do not bode well for the region’s water supply.
According to a 2005 department of agriculture report, the Western Cape “is likely to become warmer and drier over time… [with] reduced water in the rivers”.
Also in December last year, water affairs said any increase in demand for water had serious implications, “as the next augmentation project may well have to be fast-tracked to ensure an adequate supply of water to every city, town and industry that gets its water from the WCWSS”.
According to City of Cape Town statistics, “migration growth” is about 16 000 households a year, compared to the city’s “natural growth” rate of 11 000.
Working on an estimated five people per household, this means the city’s population is growing by about 135 000 people a year, of whom about 80 000 are migrants.