What a shared supply is
Sometimes a single supply pipe leaves one outside stop valve and then splits to feed two, three or more houses. Thames Water say this "is more common when buildings are close together, such as on a terraced street", which is most of inner London built before the First World War. Whole terraces were plumbed from one connection, and many of those arrangements are still in service, now with a plastic patch here and a lead section there.
The ownership position is short. Thames Water: "you and your neighbours have joint responsibility for maintaining the shared part of the pipe and any associated costs. We don't get involved in third party disputes." Their leakage code of practice adds the other half: you are responsible for maintaining the part of the pipe which supplies only your property. CCW put it the same way, that a shared pipe serving more than one property becomes the joint responsibility of all the property owners connected to it.
So there are two different pipes in one trench, legally speaking: the common run, owned jointly, and your spur, owned alone.
| Section | Who is responsible |
|---|
| Main and communication pipe, up to the outside stop valve | Thames Water |
| Shared run from the stop valve to the point it branches | Joint — all connected owners |
| Branch feeding only your property | You alone |
| Everything past your internal stop tap | You alone |
How to tell whether you are on one
Thames Water give a simple field test in the lead replacement guidance, and it works for any shared supply question. Look for the outside stop valve in front of your property. If you have one and your neighbours each have one, you are likely on separate supplies. If there is one valve but your neighbours do not have their own, you may be sharing. If there is no outside stop valve in front of your property at all, you may well be sharing with your neighbours.
Two other signals. If turning the stop tap outside your house changes the flow at next door's kitchen tap, the supply is shared and you have just proved it in ten seconds. And if your property is unmetered while a neighbouring house in the same terrace is metered, a shared supply is often the reason a meter was never fitted.
Why the location of the leak decides the bill
This is the practical point the whole page turns on. If the leak is on the common run, every connected owner has an interest in it and the cost is shared. If it is on the branch that only feeds number 14, it is number 14's bill. Nobody can allocate that fairly by guessing, and a trench dug in the wrong place costs money and produces no answer.
Locating on a shared supply is more involved than on a single run, because there are more pipes and the branch points are rarely recorded anywhere. What works in practice:
- Isolation and step testing. Closing internal stop valves one property at a time and watching the meter or listening at the stop tap tells you which branches are live in the loss.
- Acoustic correlation. Two sensors on accessible metal fittings at either end of a section, comparing arrival times of the leak noise, narrows the position along that section.
- Tracer gas. On a drained branch, hydrogen and nitrogen mix pushed through the pipe surfaces above the defect. It is the method that works on plastic pipe, where acoustic struggles, and it identifies which of several parallel pipes is the one leaking.
- Pipe tracing. Establishing the actual route and branch points, which on a Victorian terrace is almost never the route anybody assumed.
The deliverable that settles a neighbour dispute is not an opinion. It is a marked position, a depth, and a written record of which branch the loss is on. That is also what a documented trace is for.
Thames Water will not referee
Worth repeating because people ask: "We don't get involved in third party disputes." They will confirm there is a loss, they will serve notice on the consumer at the premises concerned, and they will expect a repair within four weeks. Who pays for it, between neighbours, is not their problem.
Section 75(2)(b) of the Water Industry Act 1991 allows the notice to be served on the consumer, and the recovery power in section 75(9) runs against "the person on whom the notice was served". So the person holding the letter carries the exposure regardless of where the leak eventually proves to be, which is another reason to establish the location quickly rather than to argue first. If it turns out the steps were not necessary, section 75(10) removes their right to recover the expenses at all.
Getting neighbours to agree
No law compels a neighbour to co-operate quickly, so this is a practical problem. What tends to work:
- Find the leak before you ask for money. A conversation about a marked position on a plan is a different conversation from one about a suspicion.
- Put it in writing to every connected owner at once. Include what was found, where, and the four-week deadline from Thames Water. Leaseholders should copy the freeholder or managing agent, who may have a repairing obligation for shared services under the lease.
- Get one quote for the whole job. Splitting a single invoice is far easier than reconciling three.
- Check insurance individually. Some buildings policies cover the supply pipe; on a shared run, one neighbour's policy may cover the lot.
- If someone will not engage, repair anyway and recover afterwards. Leaving a confirmed leak running past the deadline exposes whoever holds the notice to an enforced repair at Thames Water's contractor rates plus their administration charges.
Separating onto your own supply
The permanent fix for a troublesome shared run is your own connection. Thames Water treat this as a new water connection, quoted separately, and they are explicit that they do not offer services to separate supplies under the lead pipe replacement scheme. So if you are replacing lead and hoping to come off the shared pipe at the same time, those are two jobs and two costs — see the lead replacement scheme.
It is usually worth it where the shared pipe is lead or old galvanised iron, where a neighbour has already refused to contribute once, or where you want a meter and cannot have one while the supply is shared.
Lead, on a shared run
Shared supplies and lead pipe tend to appear together, because both are artefacts of the same era of building. Thames Water note that many older properties are served by a shared supply pipe, and that internal lead pipework or lead solder is yours to remove through an approved plumber. If the shared run is lead, replacing only your branch leaves the common section unchanged, which limits the benefit. That is a conversation to have with the neighbours before anybody digs, not after.
When not to call us
If nobody has established there is a leak at all, do the meter test first: internal stop valve off, read the meter, half an hour, read again. If the water is surfacing in the road or pavement, it is Thames Water's and you should report it. If you are a tenant, the repair is your landlord's and your job is to tell them in writing. If the shared pipe is visible and weeping at an accessible joint, a competent plumber can remake it without any of the equipment described above.
Where we are worth paying is when several houses share a pipe, one of them has a notice with a date on it, and nobody can say which branch the water is leaving. We work at £150 per hour agreed in advance, and if we do not find the leak you do not pay for the time we spent looking. The repair and the reinstatement of whatever was opened are the same firm and the same visit where access allows.
