Why supply pipes fail
A buried pipe has no moving parts and nothing to service, so when one starts leaking there is always a reason. Knowing which reason changes whether the right answer is a repair or a new run.
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The seven things that break a buried pipe
Ordered roughly by how often they turn out to be the cause on a domestic supply.
Age and material
The single biggest factor. Lead has been out of use for domestic supplies for decades and what remains is at the end of its life. Black alkathene from the middle of the last century goes brittle and splits along its length. Galvanised steel rusts from the inside until the wall gives way. On pipework of that age a repair buys time rather than solving anything, which is why ADI recommended replacing the Grantham run in full after repairing it.
Ground movement
Clay soils swell and shrink through the year, and a buried pipe moves with them. Over enough cycles a rigid material fatigues at its weakest point, usually a joint or a bend. A dry summer followed by a wet autumn is the classic trigger, which is why a run of leaks tends to arrive in the same few weeks across a whole area.
Frost
Water expands as it freezes and a pipe laid too shallow is the one it reaches. The regulations call for at least 750 mm of cover for exactly this reason. The damage is often done in a cold snap and not discovered until the thaw, when the split starts passing water again.
Somebody else’s spade
Fence posts, tree planting, a new patio, a driveway dug out and relaid, a neighbouring utility trench. Impact damage rarely leaks straight away. A nicked pipe can hold for months and then open up, by which time nobody connects the two events.
Bad jointing and poor bedding
A compression fitting that was never fully tightened, a pipe laid straight onto hardcore instead of sand, a run pulled tight around a corner. These fail early rather than late, and a leak within a few years of a new supply being laid usually points here.
Pressure
A high incoming pressure works every joint in the system a little harder, all day and all night. On the Grantham job the engineer recommended fitting a pressure reducing valve after the repair, because the pressure arriving at that property was high enough to put the internal pipework at risk too.
Tree roots and soil chemistry
Roots do not usually pierce a water pipe, but they wrap and load it, and they dry the clay around it unevenly. Aggressive or contaminated soil attacks metal pipe from the outside, which is how a copper run pinholes without ever being touched.
Which ones give you warning
Almost none of them. A supply pipe does not weep politely for a fortnight before it opens up, and there is no service interval that would have caught it.
What does give warning is the material. A house built before the seventies that has never had its supply replaced is on borrowed time regardless of what the ground has been doing, and a first leak on lead or alkathene is worth treating as notice rather than as an isolated fault.
The other useful signal is repetition. One leak is an event. A second leak on the same run within a couple of years is the pipe telling you it has finished, and at that point replacing it costs less than continuing to find faults on it.
Tell us how old the house is
With the age of the property and what the meter is doing, we can usually say what the pipe is likely to be and what finding the fault on it involves.
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