In December 2017, Dr Seona Candy drove through the vineyards of the Franschhoek Valley near Cape Town towards the banks of the Sonderend River. In the late 1970s, the waterway was dammed to create the biggest reservoir in South Africa’s Western Cape. Behind the thick walls of the Theewaterskloof Dam lay the capacity to hold 480 million cubic metres of water, nearly half of Cape Town’s water supply.