The ISO 13165-2 standard specifies a method for the determination of radium-226 in water quality, using radon measurement (Emanometry) for analysis. This method indirectly estimates the content of radium-226 by measuring the release of radon gas in water samples, because the decay of radium-226 in water generates radon gas. This standard provides a reliable test method for detecting radioactive contamination in water quality, especially for radioactive monitoring of water sources. This method can effectively assess the concentration of radium-226 in water bodies, thus providing a scientific basis for drinking water safety and environmental protection.