This document specifies a test method for the determination of iron-55 ^{(-55 Fe)} activity concentration in samples of all types of water using liquid scintillation counting (LSC). Using currently available 55 liquid scintillation counters, this test method can measure the ⁵⁵Fe activity concentrations in the -1 range from the limit of detection up to 120 mBq ^-1. These values can be achieved with a counting time between 7 200 s and 10 800 s for a sample volume from 0,5 l to 1,5 l. Higher activity concentrations can be measured by either diluting the sample or using smaller sample aliquots or both.st edition 2021-05 Water quality — Iron-55 — Test method using liquid scintillation counting Qualité de l'eau — Fer-55 — Méthode d’essai par comptage des scintillations en milieu liquide Reference number ISO 22515:2021(E) ？ ISO 2021 ISO 22515:2021(E) COPYRIGHT PROTECTED DOCUMENT ？ ISO 2021 All rights reserved. Unless otherwise specified, or required