Water reabsorption takes place in regions lll and lV of the nephron. The loop of Henle, located in regions l and ll, is responsible for the concentration of the urine by establishing an osmotic gradient in the medulla of the kidney. The collecting duct, located in regions lll and lV, is where the final adjustment of urine concentration occurs, and this is where water is reabsorbed back into the bloodstream. Therefore, the correct answer is lll and lV.
