How do I know if the leak is on my side of the boundary?

It is established by isolating at the outside stop valve and watching the meter, then pressure-testing the run from the house. If the loss stops when the property side is isolated, the leak is yours. If it carries on, it is on the communication pipe and Thames Water own it.

Will Thames Water replace my lead pipe for free?

They will replace the lead communication pipe that belongs to them, from their main to the boundary, once you have replaced the lead supply pipe on your side. Your side is yours to arrange and yours to pay for.

Can a lead supply pipe be repaired rather than replaced?

A single joint can be cut out and a new section fitted. Whether that is a good idea depends on the condition of the rest of the run. Lead that has failed once at one wiped joint has usually thinned everywhere.

What happens to my earthing if the pipe is replaced with plastic?

If the electrical installation was earthed to the metal incoming main, that earth path disappears when the pipe becomes plastic. It needs checking and, usually, an alternative earthing arrangement by an electrician. Raise it before the trench is dug.

My neighbours and I share one supply pipe. Who pays?

Thames Water say joint responsibility for the shared section falls on all the properties it serves, along with the costs, and that they do not involve themselves in disputes between neighbours. In practice it is worth agreeing the split before the work starts, in writing.

Islington

If the pipe rising at your internal stop valve is dull grey, swollen at the joints and silver when scratched, the buried run under your front garden is almost certainly lead too, and on a pre-1970 terrace the sensible response to a leak on it is usually to replace the whole run to the boundary rather than repair one joint.

Leak Fix LondonLast updated 19 September 2026

The Leak Fix London van outside a London property

Is it actually lead? Four tests, two minutes

Do this at the internal stop valve, which in most Islington terraces is in the cupboard under the kitchen sink or under the stairs, where the pipe rises out of the floor.

Colour. Unpainted lead is a dull matt grey. Copper is brown or green, galvanised steel is a lighter silver-grey with a mottled surface.
Joints. Lead joints are swollen and rounded, because two lengths were wiped together with molten solder. Compression and push-fit joints have a sharp hexagonal or moulded collar.
Scratch. Draw a coin across it. Lead marks easily and shows bright silver underneath.
Tap. A screwdriver handle on lead gives a dull thud. Copper and iron ring.

If the first 300mm above the stop valve passes all four, the run under the front garden is very likely the same material, laid at the same time by the same person. Thames Water use the same four tests and add a useful filter of their own: the scheme they run for lead is aimed at properties built before 1970.

The lead question almost never arrives as a lead question

Nobody wakes up thinking about a supply pipe. What actually happens is one of three things.

The meter creeps with every tap in the house turned off. A strip of the front garden or the tiled path stays dark and soft through a dry fortnight while everything either side of it dries. Or a letter arrives saying a leak has been found at the property and you have four weeks to deal with it.

All three point at the same buried run, and lead makes all three more likely. Lead is soft. It creeps under load, it work-hardens where it was bent during installation, and a hundred and thirty years of bus vibration and clay movement does not leave a Victorian pipe run exactly where it was laid. The failures are rarely dramatic. They are seeps at a wiped joint, or a split along the crown of the pipe where it was flattened by a stone during backfill and has been slowly opening ever since.

Where your problem starts and Thames Water's stops

Thames Water say they are responsible for the water mains and for the communication pipe that links your supply pipe to those mains. As a homeowner, you are responsible for the water supply pipe running from the boundary of your property into your home, and for all internal pipes, appliances and fittings.

In a terrace that boundary usually falls somewhere under the front garden, the tiled path or the pavement outside the railings, and nothing visible on the surface marks it. A leak eight metres from your door can be theirs; a leak two metres from it is yours. Establishing which side of the line the loss is on is the first thing worth doing on this kind of job, because it decides who pays for everything that follows.

Shared supplies make it harder again, and Islington has a great many of them: one pipe off the main feeding two, three or four houses, a legacy of how the terraces were originally plumbed. Thames Water are explicit that where a single supply pipe serves multiple properties, you and your neighbours have joint responsibility for maintaining the shared part of the pipe and any associated costs, and that they do not get involved in third party disputes. Our Thames Water pages go through what that means in practice.

Replacing the run, in a house with no side access

This is the part that makes an Islington terrace different from a suburban semi with a driveway. There is no route for a machine. The new pipe has to go in by hand, and the ground it crosses is usually a small front garden with a stone or tiled path, railings, a coal hole, and a lightwell to a lower-ground flat.

The practical sequence is a shallow hand-dug trench from the boundary to the point of entry, 25mm MDPE in place of whatever is there, a new internal stop valve, and reinstatement of the path. Thames Water's own standard for replacement is to put in 25mm where the existing pipe is 12-15mm, with like-for-like sizing on anything larger.

Two things catch people out. First, if you are relaying more than five square metres of front garden in a traditional impermeable surface that does not drain to a permeable area, that needs planning permission; permeable surfacing of any size does not. Worth knowing before the path comes up rather than after. Second, in an older house the electrical installation may be earthed to the incoming metal water pipe. Swap that pipe for plastic and the earth path is gone. That is an electrician's job and it is not ours, and it needs to happen around the pipe work, not months later.

When not to replace

Replacement is not automatic. If the pipe is copper rather than lead, if the leak is at an identifiable joint close to the house, and if the rest of the run tests sound under pressure, repairing the joint and leaving the pipe is a perfectly reasonable answer. Digging out a functioning eighty-year-old copper supply because there is a weep at one fitting is spending money on nothing.

The case for full replacement is strongest when the pipe is lead, when it has already failed once, when the run is long, or when you are going to open the ground anyway for something else. Lead that has leaked once tends to leak again somewhere else along the same tired length.

It is also worth saying plainly: if your only concern is drinking water quality rather than a leak, that is a water quality conversation with Thames Water, not a leak repair job, and their lead replacement scheme is the route to it. We are not the right first call for that.

Who is allowed to do the work

Supply pipe work is regulated. WaterSafe approved businesses carry specific training in the Water Fittings Regulations and Byelaws, hold public liability cover, and are audited; a certificate of compliance issued by an approved plumber provides a defence for a property owner challenged by a water supplier enforcing those regulations. Whoever you use, ask what they will issue you at the end of the job. A trench backfilled with no paperwork is a problem you have bought.

Our own work here is supply pipe repair and replacement, charged at £150 an hour with the rate fixed before we attend, and if we cannot find the leak you do not pay for the time we spent looking.

Frequently asked

How do I know if the leak is on my side of the boundary?: It is established by isolating at the outside stop valve and watching the meter, then pressure-testing the run from the house. If the loss stops when the property side is isolated, the leak is yours. If it carries on, it is on the communication pipe and Thames Water own it.
Will Thames Water replace my lead pipe for free?: They will replace the lead communication pipe that belongs to them, from their main to the boundary, once you have replaced the lead supply pipe on your side. Your side is yours to arrange and yours to pay for.
Can a lead supply pipe be repaired rather than replaced?: A single joint can be cut out and a new section fitted. Whether that is a good idea depends on the condition of the rest of the run. Lead that has failed once at one wiped joint has usually thinned everywhere.
What happens to my earthing if the pipe is replaced with plastic?: If the electrical installation was earthed to the metal incoming main, that earth path disappears when the pipe becomes plastic. It needs checking and, usually, an alternative earthing arrangement by an electrician. Raise it before the trench is dug.
My neighbours and I share one supply pipe. Who pays?: Thames Water say joint responsibility for the shared section falls on all the properties it serves, along with the costs, and that they do not involve themselves in disputes between neighbours. In practice it is worth agreeing the split before the work starts, in writing.

Sources

Other parts of London

No find, no fee · £150 per hour. The rate is fixed before we attend and does not rise for a difficult property, an awkward access or an evening visit. The total depends on how long the job takes; the rate cannot change.