Shared water supply with a neighbour: who pays when it leaks

If one pipe leaves the water main, passes a single stop tap at the kerb and then splits underground to feed your house and your neighbour's, you are on a shared supply. It is one of the few defects in a house where the repair bill can legitimately belong to somebody else, and where the water company will tell you, correctly, that the argument is nothing to do with them. Shared supplies are ordinary in London terraces, and they are a common reason a leak investigation stalls: the pipe is on no map, nobody owns all of it, and the deadline to fix it runs whether or not the neighbours are speaking.

What a shared supply pipe actually is

Three pipes, two owners. The water main under the road and the communication pipe running from it to the external stop tap at your boundary, usually a small boundary box in the pavement or front path, both belong to the water company. From that stop tap into the building is the supply pipe, and that is yours.

A shared supply is when one supply pipe leaves a single external stop tap and then serves two or more properties. Thames Water's position is short: where a single supply pipe serves more than one property, "you and your neighbours have joint responsibility for maintaining the shared part of the pipe and any associated costs", and "we don't get involved in third party disputes". Read that carefully. It says the shared part, not the whole pipe. That distinction is the whole of the liability question, and most people get it wrong in the first phone call.

Why Victorian and Edwardian terraces have them

A terrace was built as one job. Laying one service into the row and teeing off it four or five times was cheaper than digging separate connections through the same footpath. Thames Water still says plainly that older terraced properties are likely to have a shared water supply, and that a symptom of one is not getting enough water at peak times.

Two things came with that. The material, usually lead, which is why Thames Water's lead replacement scheme is aimed at properties built before 1970 where lead pipework is suspected; where a property qualifies the company replaces its own communication pipe with a new 25mm plastic pipe, aiming to do so within three months of qualifying, and the shared private run beyond the stop tap stays yours and your neighbours' to replace. And the absence of any drawing. A residential drainage and water search states it flatly: water undertakers usually have no record of private supply pipes, so they are not shown on the public water map, and even the communication pipe is not normally recorded on it. The run has to be found physically.

How to find out whether you are on one

Three tests, cheapest first.

Count the boundary boxes. Walk the front of the terrace. Four houses and one boundary box between them is not proof, but two boxes for six houses means at least part of the row is shared.

Do the isolation test. This is the definitive one and it takes ten minutes with a stop tap key. Run a cold tap in each house, then close the external stop tap at the boundary box. Whichever houses lose flow are on that supply. Be careful with the old brass taps in these boxes: they seize, and they can weep once disturbed, so know what you would do about a seized or leaking stopcock before you touch it. If you are metered, the other half of the picture is reading your meter with everything shut off, which tells you whether water is still passing while your house is isolated.

Watch the flow when the neighbour draws water. If your shower drops while next door fills a bath, you are probably sharing a pipe sized for tin baths and one cold tap. There is a number attached to this. The drainage and water search sets the low pressure reference level at 9 litres a minute at 10 metres head on the customer's side of the main stop tap for a single property, and 18 litres a minute at the same head for two properties on a common service pipe. A shared 15mm lead run feeding three modern bathrooms is nowhere near it.

One regulation is worth knowing, because most Victorian shared runs breach it. Schedule 2, paragraph 10 of the Water Supply (Water Fittings) Regulations 1999 requires every supply pipe serving separate premises to have a stopvalve "conveniently located to enable the supply to those premises to be shut off without shutting off the supply to any other premises", and where a pipe serves two or more premises in common, a stopvalve "to which each occupier of those premises has access". If you cannot isolate your own house without cutting off your neighbour, that is not a quirk of an old building. It is a compliance gap, and it is what makes a leak on a shared pipe awkward to investigate.

Who pays for a leak on a shared run

Liability follows the section of pipe that failed and the properties that section serves. The appendix to a residential drainage and water search works it through with four houses on one shared pipe, and the rule that comes out of it is this.

Where the leak is	Who is responsible for the repair
Between the water main and the external stop tap (communication pipe)	The water company
On the common section that carries water for every house on the run	All the properties that section serves, jointly
On the length that serves only two of the four houses	Those two properties only
On the spur running into one house	That house alone
On a pipe crossing a neighbour's land that serves only you	You, including the part under their garden

So "we split it four ways" is a negotiating position, not the law. If the failure is on the last twelve metres serving only the end two houses, the other two owe nothing. That is why a report pinning the leak to a measured point is worth more than one that says "somewhere in the front garden". Across our last 400 leak detection surveys the cause was found in 95%, and in 2% of them the water was coming from a neighbouring property rather than the one that called us. The same ownership logic applies to an underground supply pipe generally.

What the water company will and will not do

It will repair its main and its communication pipe, write to you if its own detection work finds a leak at your address, replace a lead communication pipe under the lead scheme, and consider a leak allowance for the water lost if you are metered.

It will not find your leak, repair your supply pipe, reinstate your path or adjudicate between neighbours. On flow it is blunter still: the Consumer Council for Water states that the company has no obligation to meet pressure requirements inside your external private supply pipe, "whether shared or not", or inside your property. Poor flow caused by sharing is not a compensable low pressure event.

The clock is real. Thames Water tells household customers that whether you find a leak or it confirms one at your property, "you must fix it within four weeks", and that if you do not, it will step in under section 75 and charge you for the repair. Its code of practice for non-household customers sets the equivalent window at six weeks. In an emergency it may turn the supply off until the leak is repaired. If you have had a letter, what the Thames Water leak letter means is worth reading before the deadline rather than after.

Section 75 gives the company a period of not less than seven days from the day after service, after which it may do the work itself and "recover any expenses reasonably incurred" from the person the notice was served on. Note who that is: whoever it served, not the four households in proportion. Recovering a contribution from a neighbour afterwards is your own civil matter, and the company has already told you it will not referee it.

There is a trap in that deadline that catches people on shared pipes more than anyone else, because they lose weeks trying to get agreement. One of the qualifying conditions for the household leak allowance is that the leak "wasn't fixed under Section 75 of the Water Industry Act". Let the four weeks lapse and the company does the work, and you pay for the repair and lose the rebate on the water. Delay costs twice.

How a leak on a shared pipe is traced

The method is the same as for any buried supply pipe, with one step added at the front and one at the end.

1. Map the geometry before listening to anything. Locate the external stop tap, establish which houses it feeds, find each property's internal stop valve. On a shared run that means access to two or three houses on the same visit, arranged before the engineer arrives or the survey is wasted.
2. Isolate house by house. Close each property's internal valve in turn and watch the flow or listen at the boundary box. If leak noise persists with every house shut off, the water is escaping from the common external run rather than anyone's internal plumbing. Overnight flow logging at the boundary box settles the same question when four households are drawing off one pipe and nobody agrees on who left a tap running.
3. Listen and correlate. A ground microphone follows the assumed route; a correlator on two contact points, typically the external stop tap and an internal valve, returns a distance along the pipe. This is where the missing records bite, because a correlator needs the pipe material and the length between contacts to turn a time delay into a position. Lead and iron carry the sound; modern plastic barely does.
4. Fall back to tracer gas. Where acoustics fail, usually under a concrete front path or in traffic noise, the section is drained and charged with a hydrogen and nitrogen mix that surfaces through the ground and is picked up above it. The methods are compared in acoustic, thermal and tracer gas detection.
5. Record which section it is on. On a shared pipe the survey is not finished when the leak is found. The report has to state the position measured from two fixed points and identify which properties that length of pipe serves, because that is the document the neighbours and their insurers will argue over. It is the difference between a bill you can apportion and one you cannot, and it is part of the job on any underground water leak detection survey where one run feeds more than one property.

Getting onto a neighbour's land

Check the deeds first, because many terraces already have an easement giving the right to enter and repair. If there is none and the neighbour refuses, the Access to Neighbouring Land Act 1992 lets you apply to the court for an access order. Basic preservation works under the Act expressly include "the clearance, repair or renewal of any drain, sewer, pipe or cable", and the court must be satisfied the works are reasonably necessary for the preservation of your land and cannot be carried out, or would be substantially more difficult, without entering theirs. It must refuse if the order would cause unreasonable interference or hardship to the occupier. In practice an access order takes longer than the four weeks you have been given and costs more than most supply pipe repairs, so its real value is as leverage in the conversation next door.

Separating the supply

Separating means applying for your own new water connection, so your pipe runs from its own communication pipe and stop tap to your house alone. Thames Water's published process: apply with a fittings table, a point of entry drawing and a site map, and pay a non-refundable application and design fee; the company aims to issue a quote within 28 days, valid for six months; you lay the pipework inside your own boundary, which must be laid and inspected within 12 months of the quote date; certification comes from a WaterSafe approved plumber or a water regulations inspection the company aims to attend within seven working days; connection follows within four months of the permits being agreed with the local authority or Transport for London.

There is no published price for this. The quote depends on the length of the excavation, whether the main sits under a footway or a carriageway, and what the highway permit requires, which is why the design fee and the 28 day quote exist at all. Treat any separation price quoted over the phone with suspicion.

Two things make separation worth the trouble. It ends the joint liability permanently, so the next failure on the old run is not partly your bill. And it removes a question a buyer's solicitor will otherwise raise, because the drainage and water search flags a shared private supply.

What a survey costs and what happens next

Tracing a leak on a buried supply pipe is charged at our mains rate of GBP 200 an hour. Detection inside a property is GBP 160 an hour, with a typical survey taking two to four hours. The rate is agreed before anyone travels and does not rise on the day, and it sits behind no find, no fee: if we attend a confirmed live leak and cannot locate it, the detection time is not charged. Full rates are on the pricing page.

If you are on a shared supply with a live leak and a four week deadline running, call 020 7123 8560. Tell us how many properties are on the run and whether you can get access to the neighbouring houses, because that decides how the visit is planned. We cover London out to the M25, all 32 boroughs.