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What is the best pipe for direct burial water line?

When installing an underground water line on your property, choosing the right pipe material is crucial for longevity and performance. Direct bury water lines are pipes that are placed directly into a trench without any additional protection or casing. The pipe material needs to be durable enough to withstand being buried while still effectively transporting water for years to come. In this article, we will compare the best pipe options for direct burial water line installations.

Common Materials for Direct Burial Water Lines

There are several types of pipe commonly used for direct burial water line applications:

Polyvinyl Chloride (PVC)

PVC is one of the most popular and affordable piping materials. It is available in rigid and flexible forms.

  • Rigid PVC pipes are stiff, lightweight, and easy to install. They have threaded or belled ends that can be glued or gasketed to create watertight joints.
  • Flexible PVC pipes are thin-walled and can bend around corners and curves. But they require special couplings to join sections.

PVC pipes are resistant to corrosion and have smooth interiors that resist scale buildup and biological growth. Their bell ends make proper sloping easy to achieve for good drainage. PVC is suitable for cold and warm water delivery in sizes from 1/2 inch to 24 inches.

Polyethylene (PE)

PE pipe is flexible, bendable tubing made from thermoplastic resin. There are a few types of PE pipe:

  • High-density polyethylene (HDPE) pipe is stiff, durable, and chemical-resistant. It is commonly used for direct burial water lines.
  • Cross-linked polyethylene (PEX) pipe has more flexibility and can expand and contract with temperature changes. It requires fewer joints than HDPE.
  • Polyethylene (PE) pipe is flexible tubing suitable for smaller diameter water lines of 1 inch or less.

PE pipes are joined by heat fusion, compression fittings, or special clamp-style couplings. They have complete resistance to corrosion and mineral deposits.


Copper is an effective pipe for water delivery though more expensive than plastic options. Type K copper is commonly used underground since it has a thicker wall than other types.

  • Seamless rigid copper tubes can be joined using soldered, brazed, or compression fittings.
  • Flexible copper tubing saves on joints compared to rigid pipes.

Copper has good resistance to corrosion. But acidic soils can still corrode copper over time.

Direct Burial Installation Considerations

When selecting a pipe material for direct burial, here are some important factors to consider:

Pipe Strength

The pipe must be strong enough to withstand the pressures and hazards of being buried underground. Weight of soil above the pipe can place significant loads. The pipe could also be impacted by shifting and settling soil, ground movement, or rocks in the soil. Rigid PVC and HDPE are stronger than flexible pipe options.

Joint Strength

Joints must also maintain integrity when buried. Glued, gasketed, fused, or compression joints are preferred over slip-fittings. Restrained joint PVC pipes increase joint strength.

Corrosion Resistance

Over time, surrounding soil and groundwater can corrode pipes. Plastic PVC and PE pipes have the best corrosion resistance. Copper and metal pipes are more vulnerable requiring additional coatings or thicker walls.

Ease of Installation

Rigid pipes are easier to properly align and slope in trenches. Flexible pipes can bend around corners in the trench saving on joints. Size and weight of the pipe impacts how easily it can be managed.

Thermal Expansion

Plastic pipes like PVC and PE expand and contract more with temperature changes compared to metal pipes. This must be accounted for with enough slack in the buried line.

Environmental Factors

Soil type, depth of bury, and water table level should be evaluated. Plastic pipes are more susceptible to damage if buried too shallow. Freezing temperatures also require deeper burial depths.

The Best Pipe Materials for Direct Burial Water Lines

Taking all the factors into account, here are the best pipe types to use for direct burial water line applications:

Rigid PVC

For most residential and commercial projects, rigid PVC is the ideal choice. Rigid PVC pipes have several advantages:

  • Low cost
  • High strength and pressure rating
  • Corrosion resistance
  • Smooth water flow
  • Easy assembly of watertight joints
  • Durable and long lasting (over 50 years)
  • Available in all standard sizes

Schedule 40 and Schedule 80 PVC are suitable for direct burial. Schedule 40 is thicker and more rigid for better load-bearing capacity. PVC pipe sizes range from 1/2 inch to 36 inches for residential water lines.


For large diameter water transmission lines or mains of 8 inches or greater, high-density polyethylene (HDPE) is commonly used.

  • Flexible and can be pulled through trenches in long sections
  • Heat fused joints create leak-free connections
  • Corrosion and chemical resistant
  • Good cold weather performance

HDPE pipe sizes used underground can range from 1/2 inch up to 65 inches. Overall, HDPE has a smaller pipe size range than PVC.


For small diameter lines of 2 inches or less, copper pipes can also be effective.

  • Smooth water flow
  • High strength
  • Reusable if replaced
  • Antimicrobial properties

The higher cost of copper makes it less ideal for larger water line projects. Type K copper should be used for buried applications.

Direct Burial Installation Best Practices

Proper installation of your direct burial water line is just as important as choosing the right pipe material. Here are some key installation tips:

Excavate Trench Properly

The trench should be dug wide enough for workers to safely place the pipe. Depth is based on pipe size and local frost line depth to prevent freezing. Allow for at least 2 feet of cover over the pipe.

Remove Debris

The bottom of the trench should be cleared of all rocks, sticks and sharp objects that could damage the pipe. A layer of sand or fine gravel can be added for extra bedding and to fill voids.

Slope for Drainage

Maintain a pitch or slope of at least 1/8 inch per foot to allow for drainage and prevent standing water in pipes. Sloping should follow the natural grade. Drainage considerations are especially important for PVC and PE pipes.

Allow for Thermal Expansion

Plastic pipes expand and contract more than metal with temperature changes. Leave expansion loops or offsets during installation to compensate.

Use Proper Backfill

Fill the trench carefully avoiding large rocks that could strike and damage the pipe. Native soil or gravel can be used provided there are no sharp objects. Compact backfill in layers and mound excess soil over the trench to account for settling.

Disinfect System

Before using the new water line, disinfect the system according to local codes. This typically involves flushing chlorinated water through the piping. Retain water samples for microbial testing.


Rigid PVC and HDPE are the top choices for direct burial water line applications. PVC provides an affordable and durable piping solution for most residential and commercial projects. HDPE offers added benefits for large diameter transmission mains. Proper installation practices are critical for optimizing the burial depth, slope, drainage, and backfill compaction around the selected pipe material. Following the recommendations in this article will ensure your underground water line provides reliable service and longevity.

Pipe Material Pros Cons
Rigid PVC
  • Low cost
  • Corrosion resistant
  • High strength
  • Smooth water flow
  • Watertight joints
  • Durable and long lasting
  • Thermal expansion
  • Not as flexible as other pipes
  • Flexible
  • Fusion welded joints
  • Corrosion resistant
  • Good cold weather performance
  • Limited size range
  • Thermal expansion
  • Smooth water flow
  • High strength
  • Antimicrobial
  • Expensive
  • Corrosion potential
  • Limited size range