28 January 2020
Testing has shown there is higher than normal levels of geosmin (a naturally occurring organic compound) in the raw water supply sourced from a channel in the Murray Irrigation District to supply the Numurkah Water Treatment Plant. This causes a distinct earthy taste and odour in the water.
People in our northern supply area (including Cobram, Nathalia, Barmah, etc) who are supplied with water sourced initially from the Murray River (or channels supplied by the Murray), may also be experiencing a similar issue.
The geosmin could be a result of low levels of blue-green algae (confirmed as non-toxic varieties) in the raw water, some of which are known to release geosmin, or because the raw water storage was low and while refilling it’s caused some stirring of the water.
We appreciate people’s patience and understanding while we worked to fix the issue.
Water has remained safe to drink at all times and has always met parameters set by the Australian Drinking Water Guidelines and the Safe Drinking Water Act.
We’ve steadily increased our treatment process to remove the taste and odour – our water treatment plants have powdered activated carbon dosing units – this means the geosmin can bond with the carbon and be removed from the water. Unfortunately, sometimes not all the geosmin can be removed from the water.
We’re seeing the carbon dosing run at unprecedented levels to remove the geosmin.
We’ve also been undertaking regular sampling in the channel/river supply system to monitor the water quality and adjust treatment as necessary.
The water quality has steadily improved in the past week – the past two days have seen water quality almost returned to normal and it should continue improving.
Sensitive individuals may still detect the odour of geosmin at extremely low levels as it has a taste and odour threshold of approximately 0.00001 mg/L (10 ng/L). In comparison the taste threshold for chlorine is generally considered to be between 0.1 and 0.4 mg/L.
We’ve working to resolve it as quickly as possible, however, with cooler weather and rainfall, water demand has dropped lower than usual and the water in the system has not moved through as quickly as it normally would.
We know it’s been an inconvenience for people– we’ve had water quality specialists and operational teams working round the clock to improve the supply.