This review article series on water and electrolyte disorders is based on the 'Electrolyte Winter Seminar' held annually for young nephrologists in Japan. The seminar features dynamic case-based discussions, some of which are included as self-assessment questions in this series. The second article in this series focuses on treatment of hyponatremia, a common water and electrolyte disorder frequently encountered in clinical practice. Hyponatremia presents diagnostic challenges due to its various etiologies and the presence of co-morbidities that affect water and electrolyte homeostasis. Furthermore, limited evidence, including a lack of robust randomized controlled trials, complicates treatment decisions and increases the risk of poor outcomes from inappropriate management of both acute and chronic hyponatremia. This review provides a comprehensive overview of treatment of hyponatremia for better comprehension and improved clinical practice.