Byron Shire Council has voted to progress a new water treatment plant at Lavertys Gap for Mullumbimby, while rejecting a proposal for a comprehensive investigation into long-term water supply options.

Mullumbimby's water has been sourced from the Lavertys Gap weir on Wilsons Creek since the 1940s, but the system's viability has been under review. During drought, flows in Wilsons Creek are far less than the town's drinking water demand. During flood, the water in Wilsons Creek is dirty and not possible to treat at the existing plant.

At last week's council meeting, a motion for an evidence-based investigation comparing multiple supply options, with robust community engagement, was voted down 5-4. The proposed investigation would have examined options including an off-stream storage reservoir, which could capture water from the river when there’s enough, to store for drier periods and also to act as a settling pond to address turbidity issues.

Instead, independent councillor Michael Lyon put forward a motion to progress a new water treatment plant for Lavertys Gap – despite his long-term position that Mullumbimby should connect to the Rous County Council regional water supply rather than maintain an independent local source. Debate in the chamber was limited, and it seemed a deal had been struck with independent councillor David Warth, who had previously supported the Greens' push for an options investigation. After the motion for a robust investigation was voted down, the Greens supported Lyon's motion as a better, though not ideal, alternative to having no local supply at all.

The decision to progress planning for a new treatment plant leaves several technical questions unresolved:

• The existing water treatment site at Lavertys Gap faces significant space constraints. Modern water treatment plants must meet stringent health and engineering requirements, and the extremely turbid water from Lavertys Gap during wet weather typically requires substantial settling tanks and pre-treatment facilities.
• Economic viability is also uncertain. While water from Lavertys Gap has historically been cheaper per kilolitre than Rous water, a new expensive treatment plant with potentially limited capacity could fundamentally alter this cost equation, particularly as an emergency supply from Rous will need to supplement water from Lavertys in dry periods.
• Environmental considerations were partially addressed through an amendment by Greens Councillor Elia Hauge requiring Council to plan for environmental flows in the Wilsons River during drought conditions. However, questions remain about balancing environmental needs with community water supply, and whether fish passage improvements will be incorporated.

In a statement, the Greens councillors said they will work closely with the Water and Sewer Advisory Committee and the community to ensure the next steps of investigation into a new treatment plant at Lavertys Gap are rigorous and transparent, with answers required before committing millions of dollars to infrastructure that may not be fit for purpose.

Cr. Elia Hauge, Chair of Water & Sewer Committee, Byron Shire Council said, "As an engineer, I'm frustrated that this decision was made hastily, with no guidance from either the Water and Sewer Advisory Committee or Council staff, and through a deal struck behind closed doors rather than open debate."

"While keeping a local supply option on the table is better than losing it entirely, the path we've taken is far from ideal."

"The three questions about site constraints, economic viability, and environmental flows are just the starting point – this community deserves answers before we commit millions of dollars to infrastructure that may not be fit for purpose."

"Mullumbimby's water future is too important to be decided by backroom deals. It requires rigorous investigation and genuine community consultation."