International Plumbing Code states exterior water supply system piping should ideally lie 6 inches below the frost line and not less than 12 inches under grade for best performance.
Code Requirements for Water Lines
The standard depth for water lines in the U.S. is around 36 inches, but this can vary from location to location.
Your water line must be buried at least 12 inches below the frost line to meet local code requirements. However, a minimum depth of 6 inches below the frost line is often recommended for extra security against freezing.
The top of the pipe should be buried not less than 1 foot (0.3 m) below the frost line. In those locations where frost is not a factor, the depth of cover should be not less than 2- 1/2 feet (0.8 m) to prevent mechanical damage. Pipe should be buried below the frost line when entering streams and other bodies of water.
Pipe for conveying liquids susceptible to freezing should be buried no less than 12" below the maximum frost level. Permanent lines subject to heavy traffic should have a minimum cover of 24". For light traffic, 12" to 18" is normally sufficient for small diameter pipe (typically < 3" diameter).
A service lateral installed in a PVC conduit under the backyard lawn must be buried at least 18 inches (457 mm) deep. Many utility companies require the service lateral to be installed in conduit.
High-density polyethylene (HDPE) pipe is a good choice for underground water lines because of how the pipe is connected. Rather than using joints, which can leak, or glues and cement, which can degrade over time, HDPE pipe is connected via plastic fusion.
Running a PEX line underground is beneficial because of the pipe's flexibility, temperature resistance, and lack of a need for multiple connections along its length. In areas with aggressive soil or water conditions, plastic or brass PEX fittings are recommended.
When you are digging the trench for your new waterline, be sure the waterline is 12-inches below the local frost depth, but in no case less than 2 feet underground.
Water and sewer lines are typically 3 to 4 feet deep depending on the climate, but they can be deeper. Some sewers are buried between 20 and 30 feet below the surface. You may think that the max depth utilities will be found is around 30 feet, but there are cases where they will go deeper.
Pipes vulnerable to freezing at this temperature are usually located in an unconditioned attic, basement, crawlspace, or along an exterior wall. Underground pipes can also freeze.
My recommendation is to bury sprinkler lines 8-12 inches. I usually try to keep a standard depth of 10" because it provides more safety if I need to do some type of ground work so I don't have to worry about hitting lines.
The line varies by latitude, it is deeper closer to the poles. The maximum frost depth observed in the contiguous United States ranges from 0 to 8 feet (2.4 m). Below that depth, the temperature varies, but is always above 0 °C (32 °F).
Eighteen to 24 inches is fine in most cases.
Generally, this clause requires a minimum depth of 300 millimetres unless the water service is subjected to vehicle loading which would requires a greater depth of between 450 millimetres and 750 millimetres dependant on the above ground surface. other services including gas or electrical and drainage pipes.
The Lifespan of a Water Line
The mainline provides homes, particularly within a suburban or urban housing development, with running water. Typically, main water line pipes last decades. Some experts estimate that they last around 70 years, though this can vary from development to development.
Spoke with my colleague: California Plumbing Code 2007 Edition (news to me): Section 609.1 states: Minimum cover shall be 12" below finish grade or minimum 12" below the local frost depth. So, 18" below finish grade will be fine and I know on occasion, you get frost in Danville (rarely).
Typically, water lines are buried at a depth ranging from 18 inches to 5 feet, depending on various factors such as local climate, soil conditions, and the type of water system in place.
It is recommended to use a 'blank cap end' (made from plastic or rubber) with a purpose-made hole with a grommet to allow the water pipe to pass through. The water pipe should be laid at depth of 750mm (minimum) to 1350mm (maximum). Trenches should be lined and backfilled with sand or soft earth, not rubble.
PVC (polyvinyl chloride) is a durable plastic pipe that is highly resistant to corrosion and impact damage. The material doesn't melt easily, which works well for underground water lines. PVC pipes also come in different diameters, so it is easy to find the right size for both residential and commercial applications.
PEX Pipe Class Action Lawsuits
A number of manufacturers, including Uponor, Viega, Nibco and Zurn, have already been sued over their PEX piping products.
PEX: Due to its flexibility and durability, PEX piping should last at least 50 years. PVC / CPVC: Under typical conditions, these pipes should last up to 100 years. Keep in mind that PVC pipes are often used for drainage because extreme heat can damage them.
Microtunneling is a trenchless method that involves the use of a micro tunnel boring machine to excavate a tunnel underground. The machine is controlled remotely and uses a pipe-jacking system to install the new pipe. Microtunneling is commonly used for the installation of sewer and water pipelines.
PVC is most commonly used for drain, waste, and vent lines. It is not recommended for use in potable water lines because it can leach chemicals into the water.
PEX A offers higher burst resistance, capable of withstanding up to 500 PSI in extreme cold, while PEX B, being more rigid, is less resilient.