To prevent freezing, underground water supply pipes should be located, if possible, under?

The correct answer is to locate underground water supply pipes, if possible, under lawns. This is because lawns typically provide a natural insulating layer of soil and grass that can help maintain a more consistent temperature. The ground beneath lawns is less likely to freeze compared to locations like driveways or roads, which are often paved and can lose heat more rapidly. Additionally, lawns usually provide a thick layer of soil that can help insulate the pipes from the cold air above, reducing the risk of freezing in colder weather.

When placed under buildings, while there may be some insulation from the foundation, there is still a risk of temperature fluctuations that can lead to freezing, especially if the building is heated and creates drafts. Roads and driveways present similar challenges; they are typically made of materials like asphalt or concrete that do not insulate as effectively as soil and vegetation found in lawns. Keeping supply pipes under lawns is therefore the most effective strategy to help prevent freezing.