Toxic water supply at Mahanga

A109 Light Utility Helicopter flight with mayor Gisborne City from the air in November 2023.

A second referendum seeking support to close down a toxic public water supply at Mahanga is to be held in the coming months, with Wairoa District Council warning residents the cost to make the supply compliant will exceed $1 million.

The 70-dwelling beachside community near Mahia voted to keep the supply open in 2017, when an upgrade to make it safe was expected to cost $200,000.

But since then consultants have deemed the water from Mahanga's two bores to be of very poor quality, with arsenic, hydrogen sulphide and, during holiday periods, E.coli detected, and an indefinite boil-water notice in place.

With two new subdivisions expected to bring the number of households at Mahanga to 140, the estimated cost to upgrade the supply now exceeded $1m, said Stephen Heath, the council's community assets and services group manager.

That cost would need to be borne by households connected to the supply.

Rainwater tanks were a viable alternative, Mr Heath said, with nearby Mahia's more than 400 properties relying on tank water.

The council had already spent $70,000 on investigations into Mahanga's water supply, Mr Health said in his report to councillors.

Additionally, the impending introduction of stricter rules for drinking water in the wake of the 2016 Havelock North campylobacter outbreak made the upgrade's estimated price tag “extremely unreliable”, he warned.

That uncertainty, coupled with escalating costs, had forced the council to put on hold a similar water supply upgrade at nearby Opoutama/Blue Bay.

Wairoa district councillors voted on Tuesday to hold a referendum in 2020/21 among Mahanga ratepayers, seeking support to close it down.

At least 75 percent of voters will need to support the closure for the supply to be decommissioned, otherwise the council will be required to upgrade it.