The ISO 9696 standard specifies a method for the determination of total alpha radioactivity in water using the thick source method. This method is suitable for the measurement of all types of alpha particle radioactive sources in water, and has important applications especially in water treatment and environment monitoring. By using thick source samples, this method can effectively improve the detection sensitivity of low-concentration alpha radioactive substances. During the test, the water sample is placed through the thick source material, and the activity is determined using the counting and energy characteristics of the alpha particle radiation. The standard provides a scientific basis for water quality monitoring, helping to evaluate the radioactivity safety of water sources, ensuring public health and environmental protection.