This document specifies methods to determine 226Ra in all types of waters by alpha spectrometry. The methods are 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 after proper sampling and handling, and test sample preparation. The detection limit depends on the sample volume, the instrument used, the background count rate, the detection efficiency, the counting time, and the chemical yield. The detection limit of the methods described in this document, using currently available alpha spectrometry apparatus, is ≤ 1 mBq·l-1 (or mBq·kg-1), which is lower than the WHO criteria for safe consumption of drinking water (1 Bq·l-1). This value can typically be achieved with a counting time of 48 h for a test sample volume of 1 l. The method described in this document is applicable in the event of an emergency situation. For an emergency situation, it is preferable to reduce the counting time rather than the sample volume. Filtration of the test sample is necessary. The analysis of 226Ra adsorbed to suspended matter is not covered by this method. If suspended material has to be removed or analysed, filtration using a 0,45 μm filter is recommended. The analysis of the insoluble fraction requires a mineralization step that is not covered by this document. In this case, the measurement is made on the different phases obtained. The final activity is the sum of all the measured activity concentrations.