Which of the following factors contributes to the freezing of water mains?

The freezing of water mains is primarily influenced by the level of insulation around the pipes. Insufficient insulation allows cold air temperatures to reach the pipes, making them more susceptible to freezing. When these pipes are exposed to low temperatures without adequate protective materials, the water inside can freeze, leading to blockages and potential bursts when the water expands as it freezes.

In contrast, proximity to geothermal sources often keeps the surrounding area warmer, which can help prevent freezing. High vegetative cover may provide some insulation by trapping heat from the ground, but it is not as direct a factor as insulation itself. Seasons of excessive rainfall can cause flooding or localized saturation but do not directly affect the temperature levels that lead to the freezing of water mains. Thus, the lack of sufficient insulation stands out as the primary cause of freezing in water mains.