ISO 13163 specifies the determination of lead-210 (210Pb) activity concentration in samples of all types of water using liquid scintillation counting (LSC). For raw and drinking water, the sample should be degassed in order to minimize the ingrowth of 210Pb from radon-222 (222Rn). Using currently available liquid scintillation counters, this test method can measure the 210Pb activity concentrations in the range of less than 20 mBq·l^-1 to 50 mBq·l^-1. These values can be achieved with a counting time between 180 min and 720 min for a sample volume from 0,5 l to 1,5 l. Higher 210Pb activity concentrations can be measured by either diluting the sample or using smaller sample aliquots or both. It is the laboratory’s responsibility to ensure the suitability of this test method for the water samples tested.