**Core Concept**
Intestinal obstruction occurs when there is a blockage in the normal flow of intestinal contents, leading to a buildup of fluid, electrolytes, and waste products in the intestine. This can cause severe water loss due to the loss of intestinal secretions, absorption of water into the intestinal lumen, and impaired absorption of electrolytes.

**Why the Correct Answer is Right**
The correct answer is related to the site of obstruction. Obstruction in the small intestine (specifically, the jejunum) leads to severe water loss due to the high volume of intestinal secretions, such as pancreatic and bile juices, which are rich in water and electrolytes. The small intestine is also responsible for the majority of electrolyte and water absorption, and obstruction at this site impairs this process, leading to severe dehydration.

**Why Each Wrong Option is Incorrect**
**Option A:** Obstruction in the large intestine (colon) would lead to water loss, but it would be less severe compared to small intestine obstruction due to the lower volume of intestinal secretions and the primary role of the colon in water absorption.
**Option B:** Obstruction at the pylorus (the region between the stomach and small intestine) would lead to vomiting and water loss, but it would be less severe compared to small intestine obstruction due to the lower volume of intestinal secretions.
**Option C:** Obstruction at the ileocecal junction (the region between the small intestine and large intestine) would lead to water loss, but it would be less severe compared to small intestine obstruction due to the lower volume of intestinal secretions and the primary role of the colon in water absorption.

**Clinical Pearl / High-Yield Fact**
In a patient with intestinal obstruction, the severity of water loss is directly related to the site of obstruction, with small intestine obstruction leading to the most severe water loss.

**Correct Answer:** C.