Can I upgrade my water supply pipe, and is it worth it?

Most people arrive at this question the same way: they ran the bucket test before getting combi quotes, the flow rate came back low, and an installer said the supply pipe was the problem. So can you upgrade it, who is allowed to touch which bit, and is it money well spent?

The short answer is yes, you can almost always upgrade it, and it is your job to arrange rather than the water company's. Whether it is worth doing depends on something most people get wrong, which is the difference between flow and pressure. Start with the ownership, because that is what decides who pays for what.

Who owns which length of pipe

There are three pipes between the water main in the street and your kitchen tap, and Ofwat sets out plainly who is responsible for each.

• The water main. The company's, always. Usually under the road.
• The communication pipe. Runs from the main to the boundary of your property. The company's responsibility, and where an external stop tap has been fitted in the footpath, that stop tap normally marks the end of their pipe and the start of yours.
• The supply pipe. Runs from the boundary to the first fitting or stop tap inside your house. Yours. Every stop tap and fitting along it is yours to maintain too.

The detail that catches people out is that the supply pipe stays yours even where it runs under the highway or across land you do not own. Length has nothing to do with it. A house set well back behind a long front garden can own thirty metres of pipe it has never seen.

The second trap is the shared supply pipe. In older terraced and Victorian streets, one pipe often serves several houses off a single connection, and Ofwat is clear that a shared supply pipe is the joint responsibility of all the properties it serves. That matters twice: you cannot simply upgrade a pipe that is not solely yours, and you are sharing whatever flow it delivers with everybody on it. If your test reads fine at ten in the morning and badly at seven in the evening, a shared pipe is a strong suspect.

Source: Ofwat, responsibility for pipes and pumping stations

Check the pipe is actually the problem first

Before anyone digs a trench across your front garden, be sure the restriction is underground. It very often is not.

The usual culprits inside the house are a main stop tap that has been half closed for years and seized there, old 15mm internal runs with a lot of elbows, scaled or corroded copper on a hard water supply, and isolating valves under sinks that were never fully opened. All of those look exactly like a low flow rate at the tap and none of them need a digger. A decent plumber can work out where the flow is being lost by testing at successive points along the run, starting at the first tap after the stop tap.

Test at different times of day too. A supply that only struggles at peak times is telling you about demand on a shared pipe or a stretched main, not about your pipe's diameter.

What an upgrade actually involves

A supply pipe upgrade means replacing the buried run from your boundary to the house with new blue MDPE, typically 25mm for an ordinary home, in place of whatever narrow lead, iron or copper is down there now. It is groundworks more than plumbing, and the rules around it are specific.

Under the Water Supply (Water Fittings) Regulations 1999 the new pipe has to be buried at least 750mm below finished ground level and no more than 1350mm. Shallower or deeper than that band needs the water company's agreement, and that is a notifiable job rather than a judgement call on site. Where the run crosses a driveway it wants more cover than a garden run. Materials and fittings must be approved for drinking water, and where the pipe enters the house it needs ducting and protection rather than being bedded straight into masonry.

What drives the cost of the job is not the pipe. It is the length of the run, what is sitting on top of it, and what else is buried alongside it. Thirty metres under a block paved drive with a gas main and a BT duct in the way is a completely different job from eight metres across a lawn. Impact moling can pull a new pipe through without a full open trench where the ground allows it, which is why a good contractor looks at the route before quoting anything.

Source: Water Supply (Water Fittings) Regulations 1999

Do both halves at once, and ask about lead

This is the single most useful thing on this page. If you are replacing your own supply pipe, tell your water company before you start, because they may replace their side at the same time. WaterSafe's advice is exactly that: contact your local water company, as they may be able to replace the pipes beyond your house and garden.

In Northampton and Milton Keynes that is Anglian Water, and their position is published. They say that if your existing service is made from lead, you may qualify for their side of the pipework to be replaced free of charge or at a reduced cost, and that if you replace your pipes you should let them know so they can make sure the pipe leading to your home is not lead either. Replacing your half and leaving a lead communication pipe feeding it is the worst of both worlds, and it is avoidable with a phone call.

Lead is worth checking for on its own account. Anglian say it is more likely in homes built before 1970, and pipework installed before 1987 may have lead soldered joints. Unpainted lead pipe is dull dark grey, its joints look swollen, it gives a dull thud rather than a ring when tapped, and a gentle scrape with a coin shows a shiny silver streak. If you are unsure, they run a lead advice line and will test the water.

Source: WaterSafe, who is responsible for lead pipe replacement; Anglian Water, lead in drinking water

The honest bit: a bigger pipe is not a pump

Here is where a lot of homeowners are quietly misled. Widening the supply pipe reduces the friction the water fights on its way in, so it recovers flow. It does not create pressure. If the pressure available at your boundary is genuinely low, a 25mm pipe will deliver more litres a minute than a 15mm one, but it cannot lift the pressure above what the network is giving you in the first place.

So the test that matters is what the supply does at the boundary, not just at the kitchen tap. If the flow improves markedly when measured close to where the pipe enters the property, the restriction is inside and the dig will not fix it. If it is poor right at the entry point, the pipe or the connection is worth attacking. Any contractor confident enough to quote without establishing which of those is true is guessing with your driveway.

When it is worth doing, and when it is not

Worth doing when the existing pipe is lead, when it is shared with neighbours and you can get your own dedicated connection, when the run is genuinely narrow original pipework, and when you want a large combi or an unvented cylinder that will not perform on the supply you have. Worth doing sooner rather than later if the ground above it is about to be landscaped or paved, because digging a new drive up in three years costs far more than routing a pipe under it now.

Not worth doing when the pressure at the boundary is the limit rather than the pipe, when the restriction turns out to be inside the house, or when a system boiler and a hot water cylinder would solve the same problem without groundworks. Storing hot water is the traditional answer to a weak mains supply and it is still a good one, which is why the conversion decision and the flow rate test belong together.

Who should do the work

Use a contractor approved for water fittings work. WaterSafe approved plumbers are qualified to work to the Water Fittings Regulations and to use approved materials, which matters on a pipe carrying drinking water into your house. Your water company's connections team will also tell you how they want the new pipe presenting at the boundary, and getting that conversation done before the trench is open saves a second visit.

Around Northampton, the older terraces are where this comes up most: narrow original supplies, shared runs, and front gardens or alleys that make the route awkward. Newer Milton Keynes estate stock is usually already on modern MDPE at a sensible size, so if flow is poor there, look inside the house first.

Get the boiler side priced properly

If a low flow rate is what started all this, get the heating decision and the pipe decision quoted together rather than separately. Tell us about the job and we will put you in touch with three vetted local installers who will measure the actual flow at your property before recommending a boiler, instead of promising a performance your supply cannot deliver.