**Core Concept**
The kidneys play a crucial role in maintaining water balance in the body through the reabsorption of water from the filtrate back into the bloodstream. This process is essential for maintaining proper hydration and electrolyte balance, particularly in the context of hypernatremia, where the body has an elevated sodium level.

**Why the Correct Answer is Right**
In the context of hypernatremia, the kidneys must reabsorb water to dilute the sodium concentration in the blood. The majority of water reabsorption occurs in the proximal convoluted tubule (PCT), where approximately 65-70% of the filtered water is reabsorbed back into the bloodstream. This is achieved through a process called passive reabsorption, where the water molecules follow the osmotic gradient created by the reabsorption of solutes such as glucose, amino acids, and sodium. The PCT is highly permeable to water, and the presence of aquaporin-1 channels facilitates the rapid movement of water molecules across the tubular epithelium.

**Why Each Wrong Option is Incorrect**
**Option A:** The distal convoluted tubule (DCT) does contribute to water reabsorption, but to a much lesser extent than the PCT. The DCT is less permeable to water and relies on the reabsorption of sodium and chloride ions to create an osmotic gradient for water reabsorption.
**Option B:** The collecting duct is not primarily responsible for water reabsorption. While it does play a role in water reabsorption under the influence of antidiuretic hormone (ADH), the majority of water reabsorption occurs in the PCT.
**Option C:** The loop of Henle is involved in water reabsorption, particularly in the thick ascending limb, but it is not the primary site of water reabsorption in the normal kidney.

**Clinical Pearl / High-Yield Fact**
In the context of hypernatremia, the kidneys must work to reabsorb water to dilute the sodium concentration in the blood. This process is most efficient in the proximal convoluted tubule, where approximately 65-70% of the filtered water is reabsorbed back into the bloodstream.

**Correct Answer: C. Collecting duct is not the primary site of water reabsorption.