Wellington's water supply under microscope

Fears that the toxic poison 1080 could leach into catchment rivers and contaminate the region's water supply have forced the extended closure of the Wainuiomata water treatment plant.

Greater Wellington Regional Council has been carrying out regular testing for 1080 in the Wainuiomata and Orongorongo rivers since a major poison drop in the forested catchment area behind Wainuiomata in early August.

Utility service acting divisional manager Murray Kennedy said 1080 pellets were dropped there every five years to kill possums.

The pellets needed about 100 millimetres of rain to break down. But a particularly dry winter meant not enough rain had fallen to safely disperse the poison.

While no traces of 1080 had been detected in waterways during testing, the plant had remained closed for the last two months -- about a month longer than expected -- as a precaution.

It supplies about 20 per cent of the region's water. Water plants at Waterloo and Te Marua have been drawn on to meet demand.

Mr Kennedy said the extended closure, while unplanned, had not affected Wellington water supplies or created shortages.

"It's just normal operations. We expected about a month, it's taken two, but it's not creating any constraints on the system."

The Wainuiomata plant was expected to reopen in the next week.

- NZPA