To establish causality there is a need for more intervention
studies, as data based on physiological measures of hydration
status are difficult to interpret. In a German survey children who
were more hydrated drank more water, ate more water-supplying
foods and consumed less energy from fat (Stahl, Kroke, Bolzenius,
& Manz, 2007). It seems that the well-hydrated child tends to have
an overall better diet, making it impossible to attribute any
difference in cognitive functioning to a lack of water rather than
generally poorer nutrition. However, the present findings should
be generalized with caution as there is yet a very small evidence
base and we await the findings from similar studies that establish
in children of different ages the water intake that is required for
optimal cognitive functioning.