This document describes a test method for the determination of radon-222 (222Rn) activity concentration in non-saline waters by extraction and liquid scintillation counting. The 222Rn activity concentrations, which can be measured by this test method utilizing currently available instruments, are above 0,5 Bq·l−1 which is the typical detection limit for a 10 ml test sample and a measuring time of 1 h. It is the responsibility of the laboratory to ensure the validity of this test method for water samples of untested matrices. Annex A gives indication on the necessary counting conditions to meet the required detection limits for drinking water monitoring.