Merriwa Water Supply

NSW Health has advised that results above screening values do not mean the drinking water is unsafe. UHSC will keep the community updated with any new information. The Australian Drinking Water Guidelines use a reference level of 1mSV per year. As a comparison, the normal level of background radiation that most people are exposed to is approximately 2mSv per year and some medical investigations such as CT scans may deliver a dose as high as 10mSv. However, efforts should be made to reduce exposure where feasible if the annual radiation dose in drinking water is found to exceed 1mSv . As a precaution, Upper Hunter Shire Council is switching to using the two bores with the lowest radiation levels.

A radionuclide is an unstable form of an atom that changes to form a more stable atom, emitting particles called radiation. In Merriwa’s case, it involves Alpha and Beta particles, which are from naturally occurring sources. 

Radioactive materials occur naturally in the environment and everyone is exposed to low levels of radiation. Some minerals that emit radiation can be present in drinking water and typically contribute a small amount to overall exposure to naturally occurring radiation. The radiation comes from the underground rock material that is in contact with the water. 

NSW Health has advised that results above screening values do not mean the drinking water is unsafe. Further testing will provide more detailed information. NSW Health advises that the level of radiation is unlikely to pose a health risk NSW Health have assessed the maximum possible dose based on the current screen level results to be approximately 2mSv/year (milliSievert is a unit of radiation dose). The dose of radiation will be accurately calculated when the radionuclides in the water have been measured.  Standard medical diagnostic equipment such as CT scans can deliver a dose as high as 10mSv.

Detailed radionuclide testing by the Australian Nuclear Science and Technology Organisation (ANSTO) is required, which will take approximately 10 weeks.  

These results will allow the dose of radiation from drinking the water to be calculated. Knowing the dose will allow Upper Hunter Shire Council to plan its next steps, in consultation with key stakeholders (including NSW Health, DCCEEW). The community will be informed about these updates.

As a precaution, Council has switched to using the groundwater bores with the lowest radioactivity while investigations continue.

The radiation detected could originate from various materials found within the water source, and each different material gives a different dose of radiation. The activity of each radioactive material (radionuclide) in the water needs to be separately measured to gain a comprehensive understanding. This process is very time consuming.