Density of water is

Water exhibits a unique property known as the anomalous expansion of water. While most liquids contract and become denser as they cool, water reaches its maximum density at approximately 4°C (specifically 3.98°C) [1]. Between 0°C and 4°C, water actually contracts when heated and expands when cooled. Below 4°C, the density begins to decrease because the water molecules start forming an open hexagonal crystal structure as they transition toward ice. This density anomaly is critical for aquatic life, as the denser 4°C water sinks to the bottom of lakes and ponds, while the less dense ice forms at the surface, providing insulation for the liquid water below [1]. Consequently, the density of water is at its peak at 4°C.

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC4686860/