The fact that water is densest at 4C is of great Importance in nature -IOC Ice C Liquid water 4C Figure 8.12 As water cools to 4C, it sinks. Then, as water at the surface is cooled to below 4C, it floats on top and can freeze. Only after surface ice forms can temperatures lower than 4C extend down into the pond. This does not happen very readily, however, because surface ice insulates the liquid water from the cold air.The fact that water is densest at 4℃ is of great importance in nature