Many London terraces and converted houses do not have a supply pipe each. One pipe comes in from the street and then splits, under a front garden, a passage or a floor, to feed two, three or more homes. It worked well enough when it was laid, but it makes a leak much harder to pin down. The meter reading, the low pressure and the wet ground are shared, so nobody can tell at first whose section is losing the water.
This guide explains how shared supplies are usually arranged, how a survey narrows a leak down to one section or one property, what each test result means, and why the neighbours and the water company usually need to be part of it.
What is a shared supply pipe?
Water leaves the main in the street through a communication pipe that ends at an outside stop tap, usually under a small cover near the boundary. Everything after that point, up to and inside the building, is private pipework. When that private pipe serves more than one property, it is a shared supply.
Common layouts include:
- Terraced houses on a common pipe. One pipe runs along the backs or fronts of several houses, with a branch into each one, sometimes passing under a neighbour's garden or kitchen.
- Converted houses. A house split into flats often kept its original single supply, with branches added inside for each flat.
- Two homes on one outside stop tap. The pipe splits just inside the boundary, so the external valve controls both.
- Mews and back-land homes. A pipe runs from the street under a shared access road to several properties.
Water companies are generally responsible up to the boundary. A private pipe that serves more than one home is normally the joint responsibility of all the owners connected to it. For flats, the lease is the document that says who looks after which pipe, so check it before assuming anything.
What are the signs of a leak on a shared supply?
They are much the same as for any supply pipe leak, with one difference: they may show up in more than one home.
- a water company letter or a meter reading that suggests a leak;
- pressure or flow dropping in several properties at around the same time;
- one home losing pressure badly whenever a neighbour runs a bath or a washing machine;
- a wet patch, sunken paving or unusually green grass along the likely pipe route;
- a hiss at a stopcock when nobody on the supply is using water.
Our guide to finding a leak on the underground supply pipe covers the general symptoms. The rest of this article is about the extra step a shared supply needs: working out where on the shared network the water is going.
Why is it hard to tell which property the leak is on?
- One meter may measure everyone. Where a shared supply has a single meter at the boundary, it records the water used and lost by every home on it.
- The routes are rarely recorded. Old shared pipes were laid before anyone drew plans, and they often run under extensions, patios and neighbouring gardens.
- Branch points are hidden. The tee where the pipe splits may be under a path, in a cellar or beneath a floor in one of the homes.
- Stopcocks do not always shut. An old internal stopcock that lets water past spoils any test that depends on it.
- Water travels. Water from a leak under one garden can surface in another, or soak away without showing at all.
How does a survey work out which section is leaking?
The method is to split the network into parts, test each part, and only then use detection equipment on the part that is losing water. A typical sequence looks like this.
- Map what is there. Find every outside stop tap, meter, internal stopcock and any intermediate valve, and note which home each one serves. Labels are often wrong, so each valve is checked by turning it and watching which taps stop.
- Check the stopcocks hold. Each internal stopcock is closed and a tap beyond it is opened. If water keeps running, that valve is passing and the test for that home has to rely on something else.
- Stop all use. Every home on the supply agrees not to use water for the test period, with cisterns and any storage tanks allowed to finish filling first.
- Read the meter with everything open. This gives the baseline loss for the whole network.
- Close the internal stopcocks one at a time. After each one is closed, the meter is read again over the same period.
- Close them all. If the meter still moves with every internal stopcock shut and holding, the leak is on the shared pipe or on a branch before it reaches a stopcock.
- Locate the leak on the section identified. Only then does the engineer trace the pipe route and use acoustic listening, a correlator or tracer gas to pinpoint the spot.
What do the test results mean?
| Result | What it suggests | Next step |
|---|---|---|
| Meter stops when one home's stopcock is closed | The water is being lost inside that property, after its stopcock | A leak search inside that home: toilets, tanks, appliances, hidden pipework |
| Meter slows but does not stop when one stopcock is closed | More than one loss, or a passing stopcock | Confirm the valve holds, then repeat for the other homes |
| Meter still moves with every stopcock closed and holding | A leak on the shared pipe or a branch before a stopcock | Trace the route and pinpoint the leak from the surface |
| Meter stops when an intermediate valve is closed | The leak is beyond that valve | Concentrate on the section the valve controls |
| Meter does not move at all | No measurable loss at the time of the test, or a meter that is not registering | Check the meter works, and consider whether the leak is intermittent |
How are the tests done when each home has its own meter?
Some shared supplies have individual meters on each branch, often fitted when metering was introduced. That helps, because each meter shows water passing into one home. If one home's meter moves while its occupants use nothing, the loss is on that branch or inside that home, and closing its internal stopcock shows which.
What individual meters cannot show is a leak on the shared section before the meters. For that, the survey compares what is entering the network with what the individual meters record, where there is a meter at the boundary, or moves straight to acoustic and tracer gas work on the shared section once the branches have been ruled out.
Why do neighbours and the water company get involved?
A shared supply cannot be tested properly by one household on its own.
- Access. The engineer may need to reach stopcocks and valves inside neighbouring homes, and to walk the pipe route through their gardens.
- Water use. A meter test only works if every home on the supply stops using water at the same time.
- Shared responsibility. Where the leak is on a section that serves several homes, the owners connected to it normally share the responsibility for repairing it. How costs are split is for the owners to agree, and deeds or leases may say more.
- Outside valves and meters. The outside stop tap and boundary meter usually belong to the water company. If they cannot be operated or read, or if the leak turns out to be on the company's side, the company needs to be told.
- Separating supplies. Owners who keep having trouble with a shared pipe sometimes ask their water company about a new, separate connection for their home. The company can explain its process and charges.
A written report that shows which section was losing water, with the readings behind it, makes those conversations easier because it replaces guesswork with evidence.
What should you do before a survey on a shared supply?
- Talk to your neighbours. Explain the problem and agree a time when everyone can be home or give access, and stop using water.
- Find your own stopcock and check it turns without force. Our guide to a leaking or stiff stopcock explains what to look for.
- Find the outside stop tap and meter, and note whether other homes appear to share them.
- Collect what you know. Water company letters, meter readings, dates when pressure dropped, and any plans or notes about the pipe route.
- Keep wet areas visible. Do not dig or fill in a wet patch before the survey, as it helps confirm the pipe route.
When should you call a leak detection specialist?
Call when the meter or the water company suggests a leak and the homes on the supply cannot tell whose section it is on, when the shared pipe runs under hard surfaces or buildings, or when the owners need an independent record before agreeing a repair. The survey combines isolation and meter tests with tracer gas or acoustic location once the section is known.
Our water mains leak detection for underground and supply pipe leaks is £300 to £500. Call 020 3912 0200 to talk through your layout before booking.
Frequently asked questions
How do I know if my water supply is shared?
Signs include one outside stop tap or meter serving more than one address, your pressure dropping when a neighbour uses water, and your stopcock not being the only one that controls your taps. Your water company may also have records for the connection.
Who pays to repair a leak on a shared supply pipe?
A private pipe that serves several homes is normally the joint responsibility of the owners connected to it. The split of costs is for the owners to agree, subject to anything in the deeds or leases.
Can a survey tell which house the leak is in?
Usually, yes. Closing each home's stopcock in turn while watching the meter shows whether the loss is inside one property or on the shared pipe, provided the stopcocks hold and everyone stops using water.
Do all the neighbours need to be at home for the test?
Not necessarily at home, but every property on the supply needs to stop using water during the test, and access to their stopcocks is often needed.
Can I get my own separate water supply?
Many owners on shared supplies ask their water company about a new individual connection. The company can explain what is involved, including the private pipework you would need to lay.
