It's tricky to choose just *four* unique properties of water, as it has many fascinating ones. But here are four that stand out, often considered essential for life on Earth:

1. High Specific Heat Capacity: Water can absorb a large amount of heat energy before its temperature rises significantly. This is crucial for regulating Earth's climate and maintaining stable temperatures in living organisms.

2. Universal Solvent: Water's polarity allows it to dissolve a wide range of substances, making it essential for transporting nutrients and carrying away waste products in living systems.

3. High Surface Tension: Water molecules are strongly attracted to each other, creating a cohesive surface that can support small objects and allows water to move through narrow spaces. This property is vital for plant life and water transport.

4. Density Anomaly: Unlike most substances, water is less dense in its solid state (ice) than in its liquid state. This means ice floats, preventing lakes and oceans from freezing solid and allowing life to thrive in aquatic environments.

These are just a few examples, and you could argue for other properties being equally important. It all depends on the specific context and what you are looking for!