I KNOW the Constitution  s152 states the duties and functions of municipalities are basic services incl water and sanitation, and Water Services Act gives the responsibility of water and sanitation to water services authorities, ie municipalities, water services providers and the Trans-Caledon Tunnel Authority, which finances and develops bulk infrastructure. TCTA built the Berg River Dam in PARTNERSHIP with the Department of Water Affairs and CoCT. This proves municipalities have a significant function, duty and responsibility for water provision. 
I also know what I warned about elsewhere on this forum - that politicians incl Zille et al tell us want they want us to believe; that more often than not they lie and, therefore, one mustn't just accept what they say, as you're doing - there's no excuse when you have the means to verify the facts. Unfortunately, like her, you and many of her/DA supporters choose to promote an untruthful narrative. And one can't debate on that basis.