A succession of heatwaves and a worsening El Niño-driven drought are raising concerns that the country's economic heartland may soon have to implement water restrictions to manage demand. Residents of Johannesburg, Tshwane and Ekurhuleni were sent alerts yesterday asking them to use water sparingly.In the Western Cape, if dam levels don't rise soon, urban areas may be hit by water restrictions.The Rand Water alert said its reservoir levels were dangerously low. It told municipalities: "Persistent high temperatures in Rand Water's area of supply continue to strain its bulk water supply system. The lack of rainfall in Gauteng is exacerbating the situation.The three cities in turn alerted their customers.On Friday, reservoirs in Gauteng were at 45%, against normal levels of between 60% and 90%.Water supply constraints are unlikely to improve in the coming months.Agri Western Cape spokesperson Jeanne Boshoff said the lack of rain in the province this past season had hit the agricultural sector hard and emerging and commercial producers were equally affected. "Wheat producers in the Sandveld region are experiencing one of the worst droughts since 1957 and some producers estimate that their losses on dry land may amount to R3-million per 800 hectares."Dams in the Ceres region were between 40% and 50% full after one of the driest winters in years, and producers were considering whether or not to plant potatoes.Boshoff said if the dam levels didn' t rise soon, residents in urban areas may face water restrictions.Cobus Olivier, a scientist at the SA Weather Service, said it expected a drier rainy season, "with quite a few dry periods in between".Already in KwaZulu-Natal half a million people are facing hunger because of deepening drought.In Cape Town, mayoral committee member for utility services Ernest Sonnenberg said the city had had "lower-than-average" winter rainfall and run-off in the catchment areas of the major dams supplying Cape Town and the surrounding region."As a result, the levels of the major dams of the Western Cape Water Supply System are lower than the city is comfortable with . The six major dams of the supply system are currently at about 74% capacity, which, though not critically low, is lower than the average over the last 20 years," he said.Water expert Anthony Turton fears South Africa could be facing a decade-long drought caused by an intense El Niño, which is believed to be behind the strongest hurricane yet in the western hemisphere, which hit Mexico at the weekend. He said poor infrastructure could make the drought worse."The problem is that there has been very limited investment in bulk water storage over the last two decades," he said. Some dams had a silt problem, limiting their effectiveness in storing water. Gauteng, he said, had better bulk water storage than the rest of the country.Limited water flow into dams could create a perfect storm for toxic blue-green algae blooms, Turton warned. The blooms are linked to raw sewage pumped into dams and rivers, which in times of drought is less diluted.But Olivier said that an "intense" El Niño would not necessarily directly influence weather in South Africa. "In 1997/98 there was an extreme El Niño, but we didn't have an extreme drought at all."Experts argue it is not just nature that causes such pressure on water supply. Leaks are a huge factor.Chris Herold, president elect of the SA Institution of Civil Engineering, said: "The first desperate step that could achieve immediate results [but also lead to inconvenience and possible economic loss to some industrial users] is for Rand Water to take it out of the hands of the municipalities and impose nighttime restrictions."In the meantime, municipalities would have to redouble their efforts to repair leaks as quickly as possible to reduce wastage...