Functional constipation (FC) is a chronic constipation for which no physiological, anatomical or iatrogenic origin can be evidenced. This condition has a high impact on a patient’s quality of life and healthcare costs. Since FC is frequently associated with low physical activity and a diet low in fiber and/or water, first-line recommendations focus on sufficient activity, and sufficient fiber and water intake. In case of inefficacy of these measures, numerous drug treatments are available, either over the counter or on prescription. Magnesium sulfate has a long history in the treatment of FC, and magnesium sulfate-rich mineral waters have been used for centuries for their laxative properties. The laxative effect of magnesium and sulfate has since been widely demonstrated. Nevertheless, it appears that no clinical studies aiming at demonstrating their efficacy in FC had been conducted before the 21st century. In this paper, we reviewed the clinical data reporting the efficacy of magnesium sulfate-rich natural mineral waters. In view of their reported efficacy and safety, magnesium sulfate-rich natural mineral waters may represent a natural treatment for FC.