Cr Jinty MacTavish said she had "serious concerns" the CCO would reduce public transparency and was unlikely to deliver promised savings of $20 million over a decade.
Cr Fliss Butcher also attacked the CCO proposal, which will be considered by councillors as part of 2011-12 pre-draft annual plan deliberations this week.
A report by Dunedin City Council water and waste services manager John Mackie recommended a CCO as the preferred option to manage the city's $1.6 billion in water assets.
"We're going to sell it one day and make more profit and privatise it."
Mr Mackie last month dismissed concerns about privatisation, saying council policy ruled out privatisation of water assets.
Cr Butcher, who spoke out against an "attempted corporate grab" of water assets at a protest last year, said she opposed any move towards corporate control.
"It should be in public ownership. People need to be in control of it, not let it be run by a big corporate."
Under the proposed structure, the CCO would manage the city's water assets using the same mix of charges and rates. About 100 council staff would switch to the new unit.
The CCO would be a separate legal entity, with its own council-appointed board, reporting regularly to the council.
Cr MacTavish was against taking decision-making one step further away from councillors and the public.
"We should be looking at promoting models that are very transparent and provide direct links - or as direct as links can be - between the public and decision-making.
"I'm absolutely not convinced that the CCO model would provide that."
Most other councillors spoken to yesterday supported establishing a CCO, albeit with some reservations.
Cr Bill Acklin said a CCO "certainly does" take direct control away from the council, but annual savings of $2 million were "significant", amounting to a 2% rates reduction each year.
Cr John Bezett said he knew of no councillor who would support water privatisation.
"I just don't believe it's an issue at all."
Cr Richard Thomson believed promised savings were "likely to be less", but still of value, and the council would retain oversight of the CCO.
Cr Lee Vandervis criticised the move, saying the case for the water CCO was an admission of "the complete ineffectiveness of current council operation".
Cr Paul Hudson said the idea needed further debate, and it was important the council "doesn't lose control in any way".
"These are assets that are owned by the ratepayers. We need to make sure the control isn't lost in any way and council's influence isn't diminished too much."
