More than half of the human body is composed of water. This water regulates body temperature, transports nutrients and metabolic products in the body and supplies the tissue and skin with moisture. Water is essential!

How much fluid does a person need?
The body continuously excretes water or steam. These losses have to be made up through food and drink. The intake amount should be approximately 30-35 ml per kg of body weight for a healthy adult. However, with extreme heat, physical activity, illness, etc., the fluid requirement increases considerably.

A person weighing 70 kg needs a regular total fluid intake (i.e. drinks plus food) of around 2 to 2.5 liters. Those who adhere to the nutritional recommendations of the Swiss food pyramid will ingest more than one liter of water from their food alone. The five servings of vegetables (up to 95% water) and fruits (80–95%) recommended daily provide a significant share. But meat and fish (65–70%), bread (35%) and cereals (12%) also contain considerable amounts of water.

One would therefore need to drink 1-2 liters per day in order to reach the recommended daily water intake. Water is generally the most sensible drink, but it can be supplemented with unsweetened drinks such as teas.
Sweetened, caffeinated and/or alcoholic beverages are luxury foods and should be consumed with caution.

Source: Food pyramid of the Swiss Nutrition Society.