This document specifies a method for the simultaneous measurement of ³H and ¹⁴C in water samples by liquid scintillation counting of a source obtained by mixing the water sample with a hydrophilic scintillation cocktail.

The method presented in this document is considered a screening method because of the potential presence of interfering radionuclides in the test sample. However, if the sample is known to be free of interfering radionuclides then ³H and ¹⁴C can be measured quantitatively.

The method can be used for any type of environmental study or monitoring.

This method is applicable to test samples of supply/drinking water, rainwater, surface and ground water, marine water, as well as cooling water, industrial water, domestic, and industrial wastewater having an activity concentration ranging from 5？Bq？l^-1 to 10⁶？Bq？l^-1 (upper limit of the liquid scintillation counters for direct counting). For higher activity concentrations, the sample can be diluted to obtain a test sample within this range.