A leak gets repaired. What decides whether the house needs repiping is the pattern and the material.
Where repair is the answer
A single leak at a fitting or from a physical cause — a nail, a freeze, an impact.
A material with life left in it and no pattern of failures.
An isolated section, such as the run through a crawl space that froze.
Where a repipe is the answer
Polybutylene. Grey plastic supply pipe from the late 1970s to the 1990s, subject to a large class action. It degrades from the inside and fails without warning. Insurers frequently decline or surcharge. This is a repipe rather than a repair item, and doing it before the failure is far cheaper.
Galvanised steel supply, in a house old enough to have it. It corrodes internally, narrowing progressively — which is why an old house has poor pressure everywhere — and it leaks at the threads. Repairing one section transfers the stress to the next.
Repeated pinhole leaks in copper, which point at water chemistry or velocity rather than at bad luck. The cause is worth diagnosing, and the pipe is at the end of its usefulness either way.
CPVC that has become brittle, cracking when disturbed.
A pattern: more than one or two leaks in a couple of years in the same material.
The access argument
Most of the cost of a repipe is not pipe. It is opening walls and ceilings, and closing them again.
That has two consequences:
Doing it in one operation is far cheaper per fixture than a series of repairs, each with its own opening and patching.
Doing it when the walls are open for something else — a renovation, a bathroom, a ceiling being replaced — is cheaper again.
A house facing a bathroom renovation and an ageing supply system should do both together, and that is the single largest saving available in this decision.
What a repipe involves
New supply lines to every fixture, usually in PEX, run through walls, ceilings and floors with the minimum number of openings.
New shutoffs at every fixture, and a manifold if that layout is chosen.
Connection to the incoming service and to the water heater with the appropriate transitions.
Testing and inspection, under permit.
Making good — drywall, texture and paint, which is a large share of the cost and which some quotes exclude.
Drainage is a separate system and is not necessarily replaced with the supply. Where the drains are galvanised or Orangeburg, that is its own decision.
Living through it
A whole-house repipe in an occupied home takes days, with water off for parts of them and openings in walls throughout.
Households that can be elsewhere generally are. Where that is not possible, a good contractor phases it to keep at least one bathroom working, which is worth asking about.
Comparing quotes
Ask each contractor for the same scope in writing: which material, home-run or trunk and branch, how many openings, whether drywall repair and paint are included, whether new shutoffs and supply hoses are included, and whether the permit is included.
The last two items are where quotes most often differ, and the cheapest quote is usually the one that leaves the making-good to the homeowner.
What it is worth at sale
A documented repipe in an old house removes a standard inspection finding and a standard negotiating item.
It is rarely recovered dollar for dollar and it removes an objection every buyer would otherwise raise — which for a house being sold within a few years is most of the value.