The Korean government agency Kores intends to lodge renewed plans next year for a longwall coal mine beneath the valleys - which are the source of 53 per cent of the Central Coast's water reserves - and part of Tuggerah Lakes.

The proposed Wallarah 2 coal mine in Wyong was expected to extract 5 million tonnes of thermal export coal a year and operate around the clock.

The initial mining plan was rejected by the Labor government in March, shortly before the state election.

That rejection was despite a recommendation from the government-appointed Planning Assessment Panel that the mine be approved.

The government cited unresolved concerns over "mine subsidence, water, ecological and heritage impacts" as reasons for the refusal.

Kores said that the refusal was not made on the grounds of potential impact on the region's water supply.

In the Wallarah 2 Coal Project newsletter, the company said: "The minister's written decision did not cite water supply among the reasons for refusal."

"The project team has assessed the reasons for refusal which mainly relate to a lack of detailed information about subsidence, ecology and archaeological impacts in the most westerly area of the mine plan."

Wyong Shire Council's deputy mayor Sue Wynn said longwall mining beneath the valleys would threaten the region's water supplies and possibly contaminate Wyong River.

"Some hydrologists have said very plainly that the mine would pose a risk to the aquifers delivering water to the river and if they (the aquifers) are destabilised and disappear they may never return," Cr Wynn said.

The shire's northern residents had suffered long enough from the environmental effects of coal-fired power stations, she said.

Meanwhile, shadow minister for the Central Coast and Deputy Opposition Leader Linda Burney said the O'Farrell government had broken its promise to protect Central Coast waterways by admitting it would reconsider the mining proposal.