What is the highest density of water observed at?

The highest density of water is observed at 4°C. At this temperature, water molecules are densely packed, which is unusual compared to many other substances where density typically increases with lowering temperature. The unique properties of water arise from its hydrogen bonding, which causes it to expand slightly as it freezes.

As water is cooled from higher temperatures, it becomes denser until it reaches 4°C. Below this point, as water continues to cool toward freezing, it starts to become less dense and expands due to the structure of ice formation. This phenomenon is crucial for aquatic life, as it allows ice to float on water, creating an insulating layer that sustains life beneath.

In comparison, at temperatures like 0°C, 10°C, or 39°F, the density of water is lower than at 4°C because either these temperatures are above 4°C or are cooling beyond that point. Understanding this property of water is essential for various applications in environmental sciences, engineering, and water treatment.