Biofilm builds up in Foxton water after increased demand over summer

The biofilm was created by a chemical reaction in the treatment plant over previous years.

In order to flush the water, the fire hydrants are opened up and water discharged from them until it runs clear.

Searle said the flushing may not get rid of all the biofilm in the system.

"I would hope they would all be discharged from the fire hydrants but reality is that some may still remain in the reticulation as percentage of biofilm removal depends also on the distance between flushing points and how long each flushing session goes for."

However, a full scouring programme was scheduled for February to clean the biofilm from the water supply network. This would "dramatically" reduce any dirty water issues, he said.

The council warned that as a result of this work water users may experience low water pressure or discoloured water during and a few days after the flushing. The flushing could also cause staining of clothing during washing, the council said.