Brisbane’s water supply will be fluoride-free while the local water authority determines what caused a sudden spike in concentration.

A spokesperson for SEQWater said the Mt Crosby water treatment plant had shut down the part of the plant that adds fluoride to the city’s water, after measurements showed the concentration had doubled.

The disruption does not pose a health risk, an SEQWater spokesman said after notifying The Queensland Water Supply Regulator, and that the elevated levels of fluoride had not made it into drinking supplies.

Under the Water Fluoridation Regulation 2008, SEQWater is required to produce fluoridated water of between 0.7mg/L and 0.9mg/L averaged over three months, the company says it is still on track to meet the average for the July-September quarter.

It has been an opportunity for some who are opposed to fluoridated public water to call for the plant not to be turned back on at all, with one Brisbane MP calling fluoride “a toxic waste product.”

Queensland Health Minister Lawrence Springborg and Education Minister John-Paul Langbroek, a former dentist, have both presented views utterly in favour of further water treatment.

Reports today say SEQWater will not turn the plant back on until they work out what has gone wrong, which has not yet been determined.