Here's why:

* Solvent Properties: Water's polarity allows it to act as a universal solvent. This means it can dissolve a wide variety of substances, including salts, sugars, and proteins. This is crucial because:

* Cellular Processes: Many biological reactions occur in an aqueous environment. Water acts as a medium for transporting nutrients, removing waste products, and facilitating chemical reactions.

* Transport: Blood plasma, which carries nutrients and oxygen throughout the body, is mostly water.

* Hydrogen Bonding: Water molecules are highly cohesive due to hydrogen bonding. This creates a strong attraction between water molecules, leading to:

* High Surface Tension: Allows for the formation of water droplets and plays a role in capillary action, essential for plant water transport.

* High Heat Capacity: Water can absorb a lot of heat before its temperature changes significantly. This helps regulate body temperature.

* Reactivity: Water can participate in chemical reactions, acting as a reactant or product. For example, hydrolysis reactions break down molecules using water.

While other properties of water like its high heat capacity and cohesive forces are important for life, polarity is arguably the most fundamental for molecular level functioning. It enables the basic processes that allow life to exist and thrive.