QUEENSLAND’S water bosses have breached health regulations again.

After two years of trying, they still can’t get the fluoride dosage right in the State’s water supplies.

After accurately dosing the water for the first time in the April-June quarter this year, water authorities bungled it again between July and September, underdosing one plant.

The Amity Point water treatment plant, which began delivering ongoing fluoride for the first time in September, received just 0.6 mg/L of fluoride.

Health regulations require the water to receive between 0.7mg/L and 0.9mg/L.

All other plants, including the the five major plants which supply 80 per cent of fluoridated drinking water to the region, delivered the right concentration.

Since fluoride was controversially first introduced into the grid in December 2008, the process has been plagued by one massive overdose and a series of underdoses.

The overdose led to residents receiving 13 times the acceptable limit of fluoride.

Authorities only have to comply on an average basis over the quarter to meet regulations, but the latest QH reports show the plants had days during the July quarter where as little as 0.01mg/L was recorded.

Water Grid spokesman Barry Dennien said he was happy all major plants had been dosed appropriately.

He said they were delivering the maximum health benefit to the community.

“It was also very encouraging to see the majority of smaller water treatment plants … meet the required concentration levels,” he said.

Opposition leader John-Paul Langbroek said it was unacceptable the water bosses still couldn’t get the dosage right in the $35 million program.

“These results raise more questions about promises the roll-out would be safe and controlled,” Mr Langbroek said.

“What we are seeing, time and time again, is water suppliers failing to meet the standards for fluoride delivery.”