Whirinaki and Esk Valley water information

The levels of manganese in the water have increased markedly since Cyclone Gabrielle. This natural mineral accumulates in the piped network, and sudden changes in water flow or increased water use can dislodge these particles, causing discolouration.

Over time, the manganese accumulates by attaching to the pipes and settling in parts of the water system. It doesn’t move until there’s a sudden change or increase in flow, which can stir up the particles and send them into the water that flows into taps.

The cyclone not only altered the topography of our region, but also impacted the source water quality of this shallow groundwater source. As a result, the Whirinaki and Esk sources now contains significantly more manganese than it did before the cyclone.

Yes, the water is safe to drink. The Whirinaki/Esk water supply is tested three times a week, and all tests confirm its safety. We acknowledge that, despite being safe, the discolouration can be unpleasant.  If your water is discoloured we advise to flush until the water runs clear or contact us if the issue persists.

Extremely high levels of manganese can pose health risks. The levels in the source water are above the Aesthetic guidelines but below the Maximum Acceptable Value of 0.4 mg/L in the Drinking Water Standards for New Zealand.  In September, the level in the Whirinaki source peaked at 0.25 mg/L with levels in the distribution remaining well below this under normal operations.  We regularly monitor the levels.

This is a complex problem to address. Similar issues have occurred in the past, such as in the Haumoana water supply and in Napier, where new sources were eventually found. The increased levels of manganese and potential solutions are included in feasibility work on long term options related to Cyclone Gabrielle damage.  Options being investigated include treatment upgrades and alternative sources. Both solutions are costly and the option of a new source relies on a suitable alternative being available within the area.  The team will report potential solutions and recommendations to Council, with any fixes likely to require additional funding through the Long-Term Plan.

A routine flushing program has been scheduled once a week on a Monday to reduce the buildup of manganese in the system. This should help prevent larger accumulations that can cause significant discolouration. Residents may notice slight discolouration afterwards and can run their taps until it clears.