Bury a water mainline in a trench that is no less than 18 inches deep. The city's municipalities office should be consulted before digging a water line trench in order to ensure that there are no electrical, water or sewer lines in the area. Metal piping is required for all water mainlines.
A water mainline is defined as any line that is under constant pressure. Furthermore, the depth of 18 inches is the measurement from the top of the pipe to the surface. This means that the diameter of the pipe needs to be accounted for when establishing the depth of the trench. Lines that run from the mainline can be placed at a depth of 12 inches. If the water line has to be buried less than 12 inches, then the piping should be made of metal to avoid accidental damage. Otherwise, polyvinyl chloride (PVC) piping can be used in place of metal.
It is also important to keep in mind the depth of the frost line of the area when establishing the depth at which to place a water line. Once the frost line is determined, the water line should be placed 12 inches below that line in order to avoid water freezing in the piping and potentially bursting the line. It is okay to place a water line above the frost line as long as the piping is flushed of water during the colder portions of the year to avoid freezing.