A. This depends on where you live. Most areas have building and plumbing codes that call out required depth for burying water, sewer, and electrical lines. If there are no codes in your area, there should still be a designated frost line depth. This is the depth at which the ground will not freeze, based on historical records and climate zone. Here in Seattle, where the climate is relatively mild, the frost depth is 12 inches. In northern Alaska where the ground is permanently frozen below a certain depth, I don’t know what they do about burying water lines.

Some local codes will call out specific requirements that exceed frost depth. You want to be sure that the line won’t freeze, and you do not want to accidentally break it when planting a tree or landscaping.