The activity per unit mass or volume of the material in which the radionuclides are essentially uniformly distributed.
The guidance levels
The guidance levels are activity concentrations in drinking-water that can be measured at an operational level by water suppliers as part of drinking-water monitoring and assessment.
The individual dose criterion (IDC)
The individual dose criterion (IDC) of 0.1 mSv y-1 is established for assessing health risks to an individual from prolonged exposure to radionuclides in drinking-water. The guidance levels have been developed as practical operational criteria to be used to assess if the IDC is exceeded.
The screening levels
The screening levels are activity concentrations that can be used to demonstrate if the IDC may be exceeded. If either of the screening levels are exceeded, the activity concentrations of individual radionuclides should be determined and compared with the guidance levels (see below).