Reefton drinking water supply investigation confirms no systemic failure
Buller District Council has completed its investigation into a non-compliant drinking water sample detected in the Reefton supply on 5 March 2026, confirming there is no evidence of a wider issue with the town’s water system.
The routine distribution sample, collected from Herald Street, returned elevated E. coli at 13.4 MPN/100 mL. MPN is a laboratory measure meaning ‘Most Probable Number’ - a statistical estimate of how many E. coli bacteria are present in 100 mL of water.
In response, council immediately activated its public health procedures, notified water regulator Taumata Arowai and Health New Zealand, and issued a precautionary boil water notice for the Reefton community.
Group Manager Infrastructure Services Anthony Blom says: “Council undertook a comprehensive source-to-tap investigation, examining all aspects of the water supply system. This included the source bore, treatment process, treated water storage, distribution network, backflow risks, sampling methods, laboratory handling, and operational activities such as hydrant use.”
The investigation confirmed that the Reefton supply continues to operate with multiple robust treatment barriers in place, including microlite filtration, ultraviolet (UV) disinfection, chlorination, and secure treated-water storage. Review of monitoring data and operational records identified no treatment failures, no abnormal source water events, and no loss of disinfection performance during the period of concern.
Extensive follow-up sampling was carried out on 5, 6 and 7 March 2026 at key points across the network, including the original Herald Street location. All repeat samples returned compliant results, with E. coli and total coliforms reported as less than 1 MPN/100 mL. These results supported the decision to lift the boil water notice on 9 March, following confirmation checks.
The investigation did not identify any confirmed contamination event within the source, treatment process, storage, or wider distribution network. While a highly localised backflow event cannot be completely excluded, the evidence indicates the most likely cause was a one-off contamination associated with the sampling point, sampling process, or environmental conditions at the sampling box. A laboratory-related factor was also considered but deemed less likely.
“An independent review by an external consultant supports these findings, concluding there is no evidence of a systemic failure in the Reefton supply and that the result most likely reflects isolated sample contamination, rather than a genuine water quality issue” explains Mr Blom.
Council has identified a number of practical improvements to further strengthen assurance and reduce residual risk. These include enhanced sampling protocols such as mandatory glove use, cleaning and refinement of sampling taps and boxes, improved documentation of field observations, sanitisation practices, prioritisation of backflow prevention work, reservoir maintenance actions, and tighter management of hydrant and standpipe use.
The investigation concludes that the event was isolated and does not indicate any ongoing risk to the safety or reliability of the Reefton drinking water supply.
“Buller District Council acknowledges the impact of the precautionary boil water notice on the Reefton community and thanks residents for their cooperation during the incident” concludes Mr Blom.
-ENDS-
For further information please contact:
Community Engagement Team
Buller District Council
Media.Enquiries@bdc.govt.nz
Disclaimer
The information in this media release was correct at time of publication. Changes in circumstances after the time of publication may impact on the accuracy of the information.