Work to return fluoride to Wellington's water has been pushed back due to the Easter break and Covid-19 related staff absences. 

Meanwhile, Wellington Water has a new concern on its hands at one of the treatment plants that remains operating. 

A screw involved in dispensing fluoride powder at the Wainuiomata facility is showing increasing signs of wear and tear. 

An independent inquiry is under way after fluoride was turned off at two treatment plants, Te Marua and Gear Island, in the region last year without residents knowing. 

Wellington Water has been "nursing" ageing and unreliable facilities for four years, meaning there might not have been effective levels of fluoride in drinking water for that time period. 

While the water company is under the microscope, it's working "at pace" to return fluoride to residents in Porirua, Wellington City and Upper Hutt. 

In an update this morning, chief executive Colin Crampton said work on the baffle curtain at the Te Marua treatment plant would have to be pushed back by a few weeks. 

A baffle curtain works by slowing the flow of water, allowing the fluoride powder time to settle and filter. This prevents the powder clumping and gives operators control of the mixing ratio. 

Divers have already been called in to assess the damage to the curtain, which is located in a reservoir the size of two Olympic swimming pools. 

However, divers need to go in a second time. 

The Easter break and staff absences due to the Omicron outbreak meant Wellington Water would have to wait to have adequate resources to undertake further work safely, Crampton said. 

"Divers will now enter the treated water reservoir in May to remove the damaged sections of the curtain and reinstall the repaired sections. Work to buy a new replacement baffle curtain is under way and we expect to have this in the next couple of months for later installation." 

Wellington Water also needs to check the entire facility. It may be the case it is unsuitable for switching back on, regardless of the repairs to the baffle curtain. 

At Gear Island, the other plant where fluoride has been turned off, design work is progressing on a new standalone facility that can be housed in a container. 

Over at the Wainuiomata facility, which is currently operating, Crampton said plant technicians have reported a fluoride powder screw is increasingly showing wear and tear. 

"We will be monitoring this situation closely. Should the facility become unreliable we will look at other options and solutions to ensure we can continue fluoridation at this plant. 

"In the meantime, we are continuing our work to increase our supply of spare parts so we can address any maintenance issues as quickly as possible."