Wellington Water staff may have deliberately misled their board members

An independent inquiry was launched last night after the company lied about when fluoridation was stopped at its treatment plants.

It told the board fluoride hadn't been put in for six weeks at one plant -- but it turns out it was stopped at their Te Marua plant in May last year.

Wellington Water Board Chair Lynda Carroll says they need to find out exactly what's happened.

She says the inquiry will look at the events leading up to the situation, at what point the board and management should have known ... and any systemic issues that caused them not to be told.