Water is, as you know the prerequisite for life on Earth. Or rather, the Earth's life forms have arisen mainly due to the unique characteristics of water. On other planets with different conditions, there may of course exist completely different forms of life. Who knows?
Water is not like many of our other elements. The solid state of water has a greater volume and lower density than its liquid form. The density is highest in the liquid state at +4 degrees Celsius.
This strange fact that the density is highest in the liquid state makes the ice float on the water, and the water around the polar areas does not bottom freeze. Along the bottom, the water is +4 degrees Celsius and the biological activity does not stop. This means that a big range of aquatic animals can find some food during the winter, which would have been impossible if the ground was covered with ice