We report here the case of a young woman, who came by herself at the emergency department, presenting with a severe hyponatremia (106 mmol/L), as shown by her initial biological report. The biological comment leads us to review the hyponatremia considering on one hand osmolarity and on the other hand volemia. Patient's tests results showed hyponatremia with hypoosmolarity and isovolemia, due to her potomania. At last, the authors expose the main guidelines for the correction of hyponatremia.