<prompt> True about free-water clearance isRegulated by ADHDecreased by aldosteroneIncreased by furosemideIncreased in hea failure  <response>: Free-water clearance denotes the volume of solute-free water that must be removed from, or added to, the flow of urine in mlmin. to make it isosmotic with plasma. CH20 V 1 - UosmPosm V is urine volume per unit time mlmin.; Uosm and Posm are osmolalities of urine and plasma respectively. During Diuresis when ADH is absent, Uosm Posm, and their ratio is less than 1. CH2O will be positive. The maximum CH2O is 15-20 Lday or 10-15 mlmin. During Anti-diuresis when ADH is present, Uosm Posm, and their ratio is more than 1. CH2O will be negative; water is being conserved. Thus, option A is correct. Aldosterone regulates total body Na content. It causes Na and water retention. Furosemide or loop diuretics inhibit NKCC transpoer NaK2 Cl- cotranspoer in thick ascending limb. This increases Na delivered to collecting ducts. Na reabsorption at this site will cause K secretion; K is lost in the urine. Thus, it is not a free-water clearance. In hea failure or renal failure, very little free water can be generated even if the urine is dilute because the GFR is decreased. Hence option D is not correct. 