**Core Concept**
Water is a poor conductor of electricity due to its unique chemical properties. It has a high dielectric constant, which allows it to form hydrogen bonds with ions, preventing them from moving freely. This characteristic makes water a poor conductor of electricity.

**Why the Correct Answer is Right**
The high dielectric constant of water is responsible for its poor conductivity. When ions are present in water, they form hydrogen bonds with the water molecules, which effectively shields them from each other. This shielding prevents the ions from colliding and moving freely, making it difficult for electricity to flow through the water. As a result, water is a poor conductor of electricity.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because water's high dielectric constant is not a result of its molecular structure, but rather its ability to form hydrogen bonds with ions.
**Option B:** Incorrect because the density of water does not directly affect its conductivity.
**Option C:** Incorrect because the viscosity of water does not play a significant role in its conductivity.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the conductivity of a solution is influenced by its dielectric constant, which can be affected by the presence of ions or other polar molecules.

**Correct Answer:** D.