In 10 years Cape Town’s population has rocketed from 2,9m to 3,7m and it will hit 4,4m in 2020. What is not growing is the city’s already precarious water supply.
“Even in a year of normal rainfall our dams are being drawn down faster than they are filling,” says Jeremy Taylor, founder of water conservation specialist Water Rhapsody. Sharing his view, Peter Johnstone of the University of Cape Town’s Climate Systems Analysis Group (CSA G) warns: “Water supply is falling below demand.”
This, says Taylor, is evident in the level of Cape Town’s six dams, which have fallen despite a 17% increase in total capacity created by the new Berg River Dam in 2009.
The six dams, reports the City of Cape Town, stood at 57,4% of combined capacity on March 19, down from 74% of five dams four years earlier. Dam levels are falling by almost 2%/week as the Western Cape faces its second year of below-average winter rainfall.
“Until the end of May and even into June it appears that the Western Cape will get very little rain,” says Johnstone. The CSAG’s forecast indicates that in March, April and May, rainfall will be 50%-80% of average, while June will see 80%-100% of average.
“Forecasts are tricky, but so far this year, our prediction of below-average rainfall has been accurate,” says Johnstone. He adds that the Council for Scientific & Industrial Research’s Western Cape rainfall forecast to June is in line with the CSAG’s. “If there is no rain by the end of March, the city must act swiftly to curb water use,” he says .
Johnstone and Taylor have a staunch ally in Shehaam Sims, the city mayoral committee member for utility services. “There’s enough water to carry us for two years but, if we have below-average rainfall, we will have a serious problem,” says Sims. “There’s no doubt about it.”
Cape Town has one water restriction in place: a ban on watering gardens between 10am and 4pm. “It’s making little difference,” says Sims, adding that neither are appeals to save water. Domestic use accounts for two-thirds of Cape Town’s water.
“Above-average rainfall between 2005 and 2010 has made people believe we do not have a problem,” says Taylor. “We face the danger of water outages being imposed to force savings.” Johnstone believes a combination of public awareness campaigns, stricter usage restrictions and a steep rise in price for users of large quantities of water are needed.
Sims says Cape Town is tackling the problem in a number of ways, among them cracking down on municipal use and monitoring the city’s reticulation system for leaks, which account for more than 15% of water use. A pilot waste water recycling plant is also in operation.
A bolder step is also mooted. “We have called for proposals for a desalination plant,” says Sims. “We are looking at a big-scale plant powered by energy from waste material.” Because of the high costs involved, neither Taylor nor Johnstone regard desalination as a practical option for a city of Cape Town’s size. “Desalinated water costs R6/kl,” says Johnstone.
Scope for increasing Cape Town’s conventional water supply is limited. The Berg River Dam was built on the last site suitable for a major dam, while seven projects mooted by the department of water affairs and the city could increase supply by around a third by 2027. At the present rate of demand growth — 2,5%/year — Cape Town’s water needs will be 45% higher by 2027. The city has a problem that only strict water conservation measures appear to have any hope of solving.