What (a) was the rationale behind the directive from her department to Umgeni Water in terms of section 74(1) of the National Water Act, Act 36 of 1998, to establish a desalination plant in the City of Cape Town, (b) were the legislative provisions she relied on when the directive was issued and (c) are the details of the progress with regard to the establishment of the desalination plant since the directive was issued?