Which pipe should I use for a buried water supply?
Which pipe should I use for a buried water supply?
Blue MDPE for potable water, in one continuous length at the required depth, with no joints under a building.
A buried water service has three enemies: frost, contamination and future excavation. Depth is the answer to the first — the standard UK requirement is a minimum of 750 mm and no more than 1350 mm, deep enough to be below the frost line and shallow enough to reach — and the same logic applies elsewhere at whatever the local frost depth is. Contamination drives the material rules: only pipe approved for potable water may be used, and where the pipe passes through contaminated ground a barrier pipe is specified because some hydrocarbons permeate ordinary polyethylene and taint the water. The third is why the pipe is blue and why marker tape goes above it. Joints belong in accessible positions, never buried under a building.
The options, ranked
| Option | Good at | Bad at |
|---|---|---|
| Blue MDPE | Colour-coded for potable water, supplied in long coils so a service can be run without joints, and tolerant of ground movement. | Not suitable above ground in sunlight or inside where fire performance matters. |
| Black MDPE / alkathene | Fine for irrigation and non-potable supply. | Not approved for drinking water; the colour is the identification, and it matters when someone digs it up in twenty years. |
| Copper | Occasionally used for short buried sections. | Corrodes in aggressive or made-ground soils and needs sleeving and protection. |
| Ducted service | Running the pipe through a duct allows replacement without excavation. | More excavation initially and the duct must be sealed and drained. |
Technique that changes the outcome
- Lay at the depth the water undertaking specifies, bedded in sand, with marker tape above
- Use one continuous coil so there are no buried joints
- Sleeve the pipe where it passes through a wall or foundation, and insulate the rise inside
- Photograph the trench before backfilling
What goes wrong
- Black or unapproved pipe for drinking water
- Joints beneath a building or a driveway
- Laying too shallow, which freezes, or too deep, which cannot be repaired
Compiled practical guidance rather than a published standard. Product formulations vary by brand and market, so read the label — and where the work is structural, electrical or gas, the regulations that apply where you are govern rather than anything here.
Other pipe questions
| For | Use |
|---|---|
| Hot and cold water | Copper or PEX for most installations — PEX is faster and more freeze-tolerant, copper is more robust and takes heat without question. |
| Waste and drainage | Solvent-weld or push-fit PVC-u or polypropylene, at the right diameter and fall — and ABS and PVC cements are not interchangeable. |
| Central heating | Copper, or a barrier-grade plastic pipe — non-barrier plastic lets oxygen into the system and corrodes it from the inside. |
| Boiler condensate | Plastic, never copper, at a generous diameter with continuous fall — and insulate any external run, because frozen condensate is the classic winter breakdown. |
| Gas | Steel, copper of the right grade, or yellow MDPE underground — and in most jurisdictions only a registered installer may do the work. |
| Compressed air | Copper, steel, stainless or a purpose-rated aluminium or HDPE air system — never PVC, which fails explosively. |
| Irrigation | Low-density polyethylene tubing with barbed fittings for drip lines, and PVC or MDPE for buried mains. |
Common questions
- Which pipe should I use for a buried water supply?
- Blue MDPE for potable water, in one continuous length at the required depth, with no joints under a building.
- What should I avoid?
- Black or unapproved pipe for drinking water Joints beneath a building or a driveway Laying too shallow, which freezes, or too deep, which cannot be repaired
Related pages
- Which pipe should I use for hot and cold water? Copper or PEX for most installations — PEX is faster and more freeze-tolerant, copper is more robust and takes heat without question.
- Which pipe should I use for waste and drainage? Solvent-weld or push-fit PVC-u or polypropylene, at the right diameter and fall — and ABS and PVC cements are not interchangeable.
- Which pipe should I use for central heating? Copper, or a barrier-grade plastic pipe — non-barrier plastic lets oxygen into the system and corrodes it from the inside.
- Which pipe should I use for a boiler condensate drain? Plastic, never copper, at a generous diameter with continuous fall — and insulate any external run, because frozen condensate is the classic winter breakdown.
- Which pipe is used for gas? Steel, copper of the right grade, or yellow MDPE underground — and in most jurisdictions only a registered installer may do the work.
- Which pipe should I use for compressed air? Copper, steel, stainless or a purpose-rated aluminium or HDPE air system — never PVC, which fails explosively.
- Which pipe should I use for irrigation? Low-density polyethylene tubing with barbed fittings for drip lines, and PVC or MDPE for buried mains.
Sources
- Typical range compiled from manufacturer specifications — At One Place