10.3.8 Summary of reference levels and screening values for radiological characteristics

For radiological characteristics, the most appropriate measure of water quality that could be regarded as a health-based reference level is the annual effective dose to a person due to ingestion of radionuclides in the drinking water. However, the effective dose is not a directly measurable quantity. Assessment of water quality is based on the measurement of radionuclide concentration (screening). This is followed, if necessary, by the calculation of dose and its comparison to a reference level. The application of this approach is described in Chapter 7.

Table 10.7 summarises the set of parameters used in determining radiological quality of drinking water.

Table 10.7 Guidance on radiological quality of drinking water

Reference level for annual dose

The total estimated dose per year from all radionuclides in drinking water, excluding the dose from potassium-40, should not exceed the reference level of 1mSv. If this reference level is exceeded, the water provider, in conjunction with the relevant health authority or drinking water regulator, should evaluate possible protective actions on a cost-benefit basis to assess what action can be justified to reduce the annual exposure.

Screening of water supplies

Compliance with the reference level for radiological quality of drinking water should be assessed, initially, by screening for gross alpha and gross beta activity concentrations. The recommended screening value for gross alpha activity is 0.5 Bq/L. The recommended screening value for gross beta activity is 0.5 Bq/L after subtraction of the contribution from potassium-40. If either of these activity concentrations is exceeded, specific radionuclides should be identified and their activity concentrations determined. The concentrations of both radium-226 and radium-228 should always be determined, as these are the most significant naturally occurring radionuclides in Australian water supplies. Other radionuclides should be identified and quantified if necessary.