An overdose of fluoride in Brisbane’s drinking water was sent to a different area to that the Queensland government first reported, and was smaller.

Premier Anna Bligh on Thursday received the initial findings of an investigation into the North Pine water treatment plant, which the government last week said sent up to 20 times the allowable fluoride dose to 4,000 homes in Brendale and Warner, in Brisbane’s north.

But the investigation by International Water Centre chief Mark Pascoe has found the overdosed water was not pumped towards Brisbane’s north as first thought, but drawn back into the plant to backwash filters after routine maintenance.

Ms Bligh told reporters the water was then sent to a nearby YMCA camp, where 211 school children were staying, and possibly reached about 400 homes in the suburb of Joyner.

In addition, the amount of fluoride was not as high as first thought.

No more than 19.6 milligrams per litre would have reached the water supply, down from the 30 milligrams first reported, but still unacceptably high.

It is the second blunder the government has made over the incident, after first telling the public the wrong date.

Ms Bligh apologised for the confusion around the incident, which has only inflamed opponents of the controversial health initiative, introduced to southeast Queensland in December.

“I do appreciate that announcements like this do cause people concern, particularly people who have health problems anyway,’ she said.

“I apologise for any unnecessary concern that’s been caused by the lack of clarity around this incident.”

No one has reported falling ill from the overdose, and visitors to the YMCA camp would only have been effected if they drank water between 8am and 9am (AEST) on April 30.

The schools have been notified, but no students reported feeling ill at the time.

Homes in Brendale and Warner, dropped from the original scare, will be contacted again, along with Joyner residents.

Mr Pascoe’s final report, which will examine why the fault occurred, will be handed down on June 26, and the North Pine plant will remain shut in the meantime.

Fluoride is being phased in to drinking water throughout Queensland, and will be available to 95 per cent of the population when the program is finished in December 2012.