Thames Water Lead Pipe Replacement Scheme: Who Pays for What

Thames Water runs a lead pipe replacement scheme. The offer is narrower than most people assume. Thames Water will replace the lead pipe that belongs to Thames Water, from its water main to the stop valve at your boundary, once you have replaced the lead pipe that belongs to you. It will not replace your pipe, and it does not put money towards it. The rest of this is what decides whether you qualify.

Who owns which piece of pipe

Two buried pipes run between the water main and your kitchen tap, with different owners. The communication pipe starts at the main and normally runs to the outside stop valve at your boundary. Thames Water owns it and says on its pipe responsibility page that it is responsible for fixing or replacing it. The supply pipe starts at that outside stop valve and ends at your inside stop valve. You own that, along with every pipe, tank and fitting inside the house.

The Drinking Water Inspectorate uses the same split and adds the point that matters: when you arrange to replace your own pipework you should tell your water company, "because they are legally required to replace their communication pipe, if it is made of lead and is at risk of contributing to the amount of lead in the drinking water supply".

How to tell whether your supply is lead

Property age is the first filter. Thames Water says lead in water pipes has been banned since the 1970s and that you are unlikely to have lead pipes if the house was built after 1970. The scheme turns that into a hard requirement: the property must have been built before 1970.

Then look, at the internal stop valve and the outside one. Unpainted lead is a dull grey. Lead joints are rounded and swollen where two pipes meet, because they were wiped by hand rather than soldered. Scratch it gently and lead shows shiny silver underneath. Tap it with something metal: lead gives a dull thud, copper and iron ring. The DWI suggests disposable gloves for the scratch test. There is more on telling the materials apart in our note on lead, galvanised and copper pipework in older London homes, and on the ownership boundary in our guide to who is responsible for an underground supply pipe leak.

If you want it settled rather than guessed, Thames Water will sample the water at your tap. Its lead page says that if you are not in a position to replace the pipe, call 0800 316 9800 and it will collect samples. Note the sentence that follows: if the samples show elevated lead, Thames Water will replace only its communication pipe. Sampling does not get your side done.

What the scheme gives you, and the word Thames Water does not use

The scheme page never says "free". It does not mention cost, charges or a pound sign at all. What it says is that if you are replacing lead pipework, Thames Water can also replace lead pipework belonging to it, provided you qualify. In practice that is a no-charge communication pipe replacement. It is not a grant or a contribution to your own trench.

The replacement is like for like in size and location. Existing 12mm to 15mm pipes are replaced with 25mm plastic, the current industry standard. If your lead supply is larger than 25mm, Thames Water matches the existing diameter.

Is a subsidy coming? Possibly, but not yet. Thames Water's AMP8 lead strategy, accepted by the DWI as an undertaking under section 19 of the Water Industry Act 1991, commits it to design and deliver consumer trials testing incentives for owners to replace their own lead pipework, with a design date of 31 December 2025 and delivery by 31 March 2030. Trials are not an offer. Your side is your bill.

The five steps, and the two that catch people out

Thames Water sets out five steps: check your supply arrangement, choose the type of plumber, check the criteria and apply, meet the water regulations, then pass the reconnection survey or have your certificate accepted. Two are where applications come apart.

The plumber decision is not cosmetic. If you use a WaterSafe approved plumber, they issue a certificate and no open trench inspection is needed; you email the certificate in. If you use an independent plumber, Thames Water must inspect the pipe while it is still lying in an open trench, before it is buried, and that inspection has to be booked. A crew that digs, lays and backfills in a single day, which is what a good groundworks team wants to do, has removed your evidence. Without a passed survey or an approved plumber's certificate, Thames Water says you cannot qualify.

The three month window runs from your application, not from your intention. One criterion is that you are planning to replace your lead supply pipe within the next three months. If the work slips past that, you submit a new application. Applying early because you are "thinking about it" wastes the window.

The other criteria are straightforward: built before 1970, you suspect lead supply pipework, you are not aware of Thames Water having already replaced the communication pipe, you will bring the new pipe to the current outside stop valve in line with it, and you have located that valve and confirmed whether the supply is separate or shared.

The trench your plumber has to produce

To pass a reconnection survey, Thames Water requires 25mm pipe or a like for like replacement; a trench between 750mm and 1350mm deep; an approved inside stop valve; the pipe insulated and ducted at the point of entry; an approved drain valve upstream from inside the stop valve; the pipe ducted or laid in soft material; the pipe laid in line with the outside stop valve with enough excess to reach it; and the pipe tunnelled underneath any brick wall rather than passing through it. Where the pipe runs via a basement or vault, wall breakthroughs are yours.

That list is why lead replacement in a terraced London street is groundworks rather than plumbing. A 750mm trench through a tiled front garden, under a boundary wall, past a gas service and an electricity duct, is most of the cost and most of the variation between quotes.

The earthing problem nobody mentions until the pipe is out

Thames Water tells you to check your earthing before you apply if you have a lead supply pipe, if the supply is single or shared, if you know where your outside stop valve is, or if the house was built before 1966. It says to contact your electricity supplier or a qualified electrician if you are unsure.

The reason is blunt. In older properties the incoming metal water pipe was sometimes doing electrical work as well as carrying water. Replace it with plastic and that path is gone. Sort it before the pipe comes out, not after the trench is backfilled. We cover the wider overlap in water leaks and electrical safety at home.

Shared supplies, which is the hard case in London

Many older London terraces are fed by one supply pipe serving several houses. Thames Water's position is that a shared supply pipe is yours and your neighbours' to maintain and replace jointly, each responsible for any branch feeding only their own property. On leaks it adds that it does not get involved in third party disputes.

You can tell a good deal from the pavement. If you have an outside stop valve and so do your neighbours, you are probably on separate supplies. If you have one and they do not, or there is none at all, sharing is likely. Thames Water asks you to call 0800 316 9800 if you cannot work it out.

The lead scheme does not separate supplies. Thames Water states that it does not offer services to separate supplies under this scheme, and gives a different number, 0800 009 3921, for moving to a single supply. That means a new water connection, priced rather than given away. In its 2026/27 charging arrangements a single 25mm connection is £6,240 in a road, £4,340 in a footpath or private road and £2,350 in unmade ground, excluding VAT, plus £750 per metre of pipe laying in the road, a £105 application fee and a £190 design fee, with a £1,575 water infrastructure charge and a £150 environmental component on top. That is the gap between a no-charge communication pipe swap and a genuinely independent supply.

If you have a leak as well as lead

Lead supply pipes are soft, a century old in places, and they leak. Most people meet this subject because a bill jumped or a patch of drive never dries out. The two problems then run on different clocks. Thames Water's pipe responsibility page says that once a leak on your property is confirmed, it is your legal responsibility to arrange the repair within four weeks. The lead scheme aims to complete the communication pipe replacement within three months of you qualifying. So a confirmed leak on a lead supply pipe pushes you into a four week repair while the no-charge half of the job sits months away. Repairing in a hurry and backfilling before anyone has inspected the trench is how people lose the communication pipe replacement.

So establish first whether there is a live loss, and which side of the boundary it is on. Our guides on reading your water meter to check for a leak and a water leak in the garden or driveway cover the checks you can do yourself, and who is responsible for a Thames Water leak covers the boundary. If you are metered and have already lost water through your own pipe, read our note on the Thames Water leak allowance.

Across our last 400 leak detection surveys we found the cause in 95% of cases. In 2% the water was coming from a neighbouring property, which on a shared supply street is not a rare answer. In 3% it was not a plumbing leak at all: gutters, roofs and other structural defects letting water in. Which of those you have changes who digs, and whether anyone needs to dig.

To settle that before you commission a trench, call us on 020 7123 8560. Standard leak detection is charged at a fixed hourly rate of £160, and a typical survey takes two to four hours, so £320 to £640 in total. The rate is agreed before we travel and does not rise on the day, and if we attend a confirmed live leak and cannot locate it, the detection time is not charged. Full rates are on our pricing page. We cover London out to the M25, all 32 boroughs.

Why replacing only half is worse than it sounds

The scheme is built around doing both halves because half a job can backfire. The US Environmental Protection Agency's Science Advisory Board reviewed partial lead service line replacements and found that they "have not been shown to reliably reduce drinking water lead levels in the short term, ranging from days to months, and potentially even longer", and that partial replacement is "frequently associated with short-term elevated drinking water lead levels for some period of time after replacement".

The mechanism is disturbance. The DWI says working on lead pipe can temporarily raise lead concentrations and that you should flush the tap for at least ten minutes afterwards. Thames Water's instructions match: while you wait for its side, run the cold kitchen tap for about two minutes before use, and on the first day after the replacement run every drinking and cooking tap for ten minutes.

What happens anyway, without you applying

Under its AMP8 undertaking, Thames Water is targeting 54,000 lead communication pipe replacements by 31 March 2030, and must proactively replace lead pipework it owns wherever lead is detected at or above 5 micrograms per litre in regulatory or operational samples at customers' taps. That trigger sits at half the legal standard of 10 micrograms per litre under the Water Supply (Water Quality) Regulations 2016.

Nationally the data is thin. The DWI recorded 53 compliance sample failures for lead in 2024 from 13,394 samples analysed, and notes that compliance sampling is capped at eight samples per water quality zone per year. Water companies have collectively declared an ambition to be lead pipe free by 2050, which makes waiting a plan with a twenty-four year horizon. If your London supply is not Thames Water, check your own company: Affinity Water covers parts of north and west London under a separate DWI undertaking with a similar commitment.

The order to do it in

Confirm the pipe material at both stop valves. Establish whether the supply is separate or shared. Check the earthing. Price an approved plumber and an independent plumber, because the inspection logistics differ. Apply only when the work is genuinely within three months. Then have the trench inspected, or the certificate issued, before anything is buried. If a leak is part of the picture, locate it before that sequence starts rather than halfway through: call 020 7123 8560.