Why must water that has moved to the interstitial fluid in the medulla be quickly removed from the interstitial fluid?

Question

Quizplus · Accepted Answer

Water reabsorption in the kidney is dependent on a concentration gradient between the interstitial fluid of the renal medulla and the fluid in the renal tubules. This gradient is created by the countercurrent multiplier system and is maintained by the active transport of ions across the walls of the ascending and descending limbs of the loop of Henle. The movement of water into the interstitial fluid dilutes the concentration gradient, reducing the ability of the kidney to reabsorb water. Therefore, the water must be quickly removed from the interstitial fluid to prevent destruction of the concentration gradient necessary for water reabsorption.

Why Must Water That Has Moved to the Interstitial Fluid