Who is affected
The affected area stretches across much of the north of the city, including the CBD, North Dunedin, Leith Valley, Woodhaugh and any area in the central city between the town belt and the harbour.
How long is the warning expected to last
The boil water notice was expected to remain until tomorrow afternoon.
The risks
Council infrastructure and networks general manager Ruth Stokes said there was no certainty about the level of risk associated with the affected water.
"In some parts it would have been reasonably diluted, but you're basically drinking water that's the equivalent of drinking it straight out of a stream or lake."
The cause
The council says it appeared untreated raw water released from the Ross Creek Reservoir on Sunday had been able to enter the city's drinking water network.
Workers had begun releasing water from the reservoir into the Lindsay Creek on Sunday, in preparation for work set to begin in the area.
Complaints were received Monday night and this morning, prompting an investigation which found an old pipe - no longer recorded on council plans - just below the reservoir.
The pipe connected to the city's drinking supply, allowing raw water back into the network.
Where to get drinkable water
Eight water tankers have been dispatched to parts of the city, including to George St Normal School and Logan Park High School, both in the affected area.
A rush means finding bottled water at supermarkets may be difficult.
Here are the locations and times water tankers will be available:
• Cnr Dundas & Montgomery Ave, from about 2pm.
• Outside Otago Museum (Main Entrance) from about 2pm.
• Outside George Street Normal School from about 2pm.
• Oval BP forecourt from about 2pm.
• The Octagon from about 12pm.
• Outside Hunters Furniture Cumberland St from about 2pm.
• Dunedin Hospital
• The council says Dunedin Hospital has also activated its own EOC, and is relying on water tankers arranged by the council to supply fresh drinking water.
• The Southern District Health Board said Dunedin Hospital is operating as normal.