[Water in summer heat, but how much?].

Insufficient drinking during summer heat may lead to dehydration, but excessive drinking, on the other hand, may also be dangerous. In dehydration, the kidneys decrease urinary secretion by maximally concentrating the urine. When this first-line defense for dehydration has been utilized, thirst will slowly appear and the dehydration will eventually be compensated by drinking. In summer heat, decreased urine volumes are thus the first sign of dehydration and need of drinking. There is thus no use of waiting for the feeling of thirst in summer heat, as rehydration is then already long overdue.