That may or may not be true. The city insists households are the largest consumers of their water supply, ie the six major dams. (In this statement the city said residents used 70% of water supply: http://www.timeslive.co.za/local/2017/01/17/Cape-Town-water-use-spikes-as-dam-levels-drop-to-42.5. It was later amended to 65%. Does this sound like they know what they're doing?) You've not cited a document for your data.