As part of the ongoing investigation into the cause of discoloured water in Cooktown, we can confirm that independent test results, received back on Monday 9 December, have identified Manganese as the primary factor.
While both iron and manganese are present, the data indicates manganese levels are currently 120 times higher than normal—an unprecedented occurrence for the Annan water supply.
Metals Analysis Manganese (Raw vs Treated)
Metals Analysis IRON (Raw vs Treated)
Key findings
- Iron levels: Although iron has spiked in the past without causing discoloured water, it is not the primary cause of the current issue.
- Manganese levels: Testing has revealed significantly elevated manganese levels, up to 120 times higher than normal, which can cause water discoloration and impart a taste.
- Health guidelines: The Australian Drinking Water Guidelines (ADWG) health limit for manganese is 0.5mg/L. Current levels remain well below this (peaking at 0.12mg/L in treated water supply), meaning the water is with recommended guidelines.
What’s being done
- Pre-chlorination treatment has been introduced at the Annan Water Treatment Plant to help remove manganese before it reaches the filters. This treatment will continue as we monitor results.
- Ongoing testing: Daily testing for iron and manganese will begin as soon as reagents arrive. This will allow Water Treatment Plant staff to closely monitor water quality and adjust treatment processes as needed.
- Catchment investigations: Data shows significantly higher concentrations of manganese in the Annan River water. This is likely linked to changes in the catchment, including landslides caused by Tropical Cyclone Jasper.
We understand the inconvenience caused by the discoloured water and are working diligently to resolve the issue. Council will continue to keep the community informed with updates as more information becomes available.
Thank you for your patience and understanding.
For any additional questions or enquiries, please contact Council by calling 4082 0500 during office hours or emailing mail@cook.ald.gov.au at your convenience.