To date, these food supplements rich in magnesium are sold without proof of effectiveness. The clinical data are very insufficient, and no oral supplementation is reimbursed. Moreover, the prescription of oral magnesium supplementation, often several intakes a day, adds to the oncology patient an over-medicalization, which can be poorly tolerated at the digestive level, and responsible for diarrhea and a lack of compliance. Oral hydration is one of the most prescribed medical advice and remains essential to combat the risk of dehydration in extreme ages. The European Food Safety Authority (EFSA) recommends in its opinion on "Dietary reference values for water" to consume 2 liters for women and 2.5 liters for men every day, all sources combined (food and beverages). The drink represent 80% of the water intake, that is about 1.5 Liter per day excluding food. However, there are multiple water marketed or distributed freely, with different compositions. Thus the quantity and quality of the mineral water consumed can influence the metabolism.