At what temperature is water densest?

Water is densest at 4 degrees Celsius due to the unique properties of water molecules and hydrogen bonding. As water cools from higher temperatures, its density increases until it reaches this optimal point. At 4 degrees Celsius, water molecules are packed closely together, maximizing density.

As water cools further below this temperature, it begins to form a structured lattice due to hydrogen bonding, which causes it to become less dense. This phenomenon is crucial for aquatic ecosystems, as it ensures that ice, which is less dense than liquid water, floats on the surface, providing insulation to the water below during colder conditions. Understanding this property of water is essential for aquatic life and for the practical applications in water treatment processes.