Water from streams, springs and boreholes should be disinfected or boiled.
The city said water from alternative sources is not safe and that the sources have not been tested by the municipality.
Xanthea Limberg, mayoral committee member for informal settlements, water, waste services and energy, said: “Should residents continue to collect water from alternative sources, it is essential from a health point of view to boil it beforehand.
“Members of the public use these water sources at their own risk.
“Ground water, spring and urban stream sources do not form part of the city’s formal water supply system.
“The only source of safe water is that from the municipality.”
Earlier this week, the City also warned residents to keep on saving water, saying the recent rainfall was not enough to end Level 4 water restrictions.
The storm of last week, which claimed the lives of four people, caused flooding and left 2500 people homeless, did very little to dam levels, increasing it by only 1.6 percent since 5 June, when dam levels stood at 19.6 percent.
The current dam level is at 21.2 percent, and with the last 10 percent of dam water not usable, dam levels are effectively at 11.2 percent, Limberg said.
She urged residents to continue to use water sparingly.