In a letter to the Otago Regional Council chairman, the group stated only two out of five installed pumps were fully operational, a report to the engineering and hazards committee said.
The other drainage pump had been out of action for 18 months with no sign of the promised new pump.
However, all three flood pumps and one drainage pump were operational, the council was told.
Environmental engineering and natural hazards director Gavin Palmer said the other drainage pump, which failed during the April 2006 flood, would be replaced with a new pump, due to arrive in Dunedin from Sweden next week, at a cost of $395,000.
Work on site had begun and if there were no delays in getting parts, it should take two to three months to be completed.
The flood pumps had been overhauled recently, to remove objects which had been affecting performance, but further maintenance work would be needed in the future.
The group had been made well aware that replacement of the drainage pump would require time for essential design and procurement to be undertaken when it met on February 28 and on May 9, Mr Palmer said.
Council chief executive Graeme Martin said the group had been totally involved in the discussions over the replacement of the pump, agreeing on a pathway forward.
It was a "serious worry" that the group felt need the need to write the letter, he said.