• total water intake;
  • free water reserve;
  • adequate water intake

In the United States and Germany, population groups show distinct differences in water metabolism. A higher intake of preformed water (fluids and food moisture) and a higher urinary volume hint towards a more favorable hydration status of the American than the German population. In the United States, the Adequate Intake for preformed water is set based on the median preformed water intake from US survey data. In Germany, physiologically founded and empirically based Guiding Values are proposed. The recommended intake of preformed and metabolic water related to energy intake ranges from 1.01 to 1.08 mL/kcal in German adults and from 1.21 to 1.31 mL/kcal in American adults.