• Anti-diuretic hormone, released from neurohypophysis,facilitates reabsorption of water from the latter parts of the renal tubule, and collecting duct, by increasing the number of aquaporins. In the absence of ADH, more diluted urine will be produced.

• Active transport of sodium in thick ascending limb of loop of Henle: creates a hyperosmotic medullary interstitium, which pulls water out of descending limb and collecting ducts and thus favouring water reabsorption.

• High osmolarity in medullary interstitium : provides gradient for water reabsorption from collecting ducts.

• Presence of aquaporins in collecting duct: allows water to move out along the osmotic gradient, thereby favouring water reabsorption.