**Core Concept**
Diabetes insipidus (DI) is a disorder of the body's ability to regulate fluids, characterized by excessive thirst and polyuria due to a deficiency in antidiuretic hormone (ADH), also known as vasopressin. This hormone plays a crucial role in regulating water reabsorption in the kidneys.

**Why the Correct Answer is Right**
The correct answer will be the clinical feature that does not accurately describe diabetes insipidus. DI is characterized by **polyuria** (excessive urine production), **polydipsia** (excessive thirst), and **elevated serum osmolality**. The absence of ADH leads to impaired water reabsorption in the kidneys, resulting in the production of large volumes of urine.

**Why Each Wrong Option is Incorrect**
* **Option A:** Polyuria is a hallmark of diabetes insipidus, making this statement true.
* **Option B:** Polydipsia is also a characteristic feature of DI, as the body attempts to compensate for the lack of ADH by drinking more water.
* **Option C:** Elevated serum osmolality is a key feature of DI, as the kidneys are unable to reabsorb water in response to ADH, leading to increased serum osmolality.

**Clinical Pearl / High-Yield Fact**
One important distinction between central and nephrogenic DI is that central DI patients will have a normal or low serum osmolality in response to water load, whereas nephrogenic DI patients will have persistently elevated serum osmolality.

**Correct Answer:** D.