The presence of osmotically active substances in urine will produce more urine for the reabsorption of water is reduced relative to Na+. This active substances primarily inhibit water reabsorption in the proximal convoluted tubule and the thin descending loop of Henle and collecting duct and regions of the kidney that are highly permeable to water.
In addition, it also extract water from intracellular compartments that result to increase extracellular fluid volume or urine output.