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Pipe Corrosion: Causes, Warning Signs and What to Do

Corroded copper pipe in a London home

Pipe corrosion is the slow chemical or physical breakdown of a pipe from the inside or outside, and in a UK home it usually shows itself as rust-coloured or blue-green water, pinhole leaks, falling pressure or damp patches. Most corroded pipes can be dealt with calmly if you act early: find where the damage is, stop any leak, and decide whether a repair or a replacement section is the sensible fix. If water is escaping now, isolate it at the stop tap and call us on a 24/7 emergency callout so the pipe is made safe and you get a fixed quote before work starts.

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TL;DR

  • Corrosion comes from the water chemistry, the pipe material, how the system was installed and how fast water flows through it. It is rarely just “old age”.
  • Warning signs: brown, orange or blue-green water, low pressure, pinhole leaks, green crusts on copper, and stains or mould on walls and ceilings.
  • Blue or blue-green water: contact your water company. Suspected lead pipes: flush the tap, ask the water company to test, and plan replacement.
  • A single pinhole is often repairable. Repeated leaks along a run, or pipes that are lead, heavily rusted or badly pitted, usually mean replacing that section.
  • We are Gas Safe registered, answer calls 24/7 across London and give a fixed price before we start.

Table of Contents

What pipe corrosion actually is

The Drinking Water Inspectorate (DWI), which regulates drinking water quality in England and Wales, describes corrosion as the partial dissolution of the materials that make up supply systems: pipes, tanks, valves and pumps. In plain terms, the metal is slowly being eaten away or dissolved into the water, and what you see at the tap or under the floor is the result.

Two things make it matter to a homeowner, landlord or business:

  1. Leaks. Corrosion thins the pipe wall until water finds a way through, often somewhere you cannot see.
  2. Water quality. Metals can end up in the water, which is why lead, copper and iron are all tracked in the DWI’s list of common contaminants and their sources.

The good news from the National Physical Laboratory’s guide to plumbing corrosion is that copper, the most common material in UK plumbing, has been used for over 200 years and in the vast majority of cases gives a long trouble-free life. Problems come from a combination of poor materials, design, installation and water quality. That is useful: it means most corrosion has an identifiable cause you can deal with.

The main types of corrosion in household pipes

Not all corrosion looks the same, and the type tells you what to do. The NPL guide sets out three that matter for copper pipework.

General corrosion

The whole inner surface wears away evenly. For copper, the DWI links it to soft, acidic water with a pH below 6.5. The result is often blue-green staining or blue water rather than a sudden leak.

Pitting corrosion

Small, deep holes form in one spot while the rest of the pipe looks fine. The NPL says pitting can show up as pin-holing from a few months to over 10 years after installation, and bacteria can play a part. The DWI associates copper pitting with hard groundwater that carries carbon dioxide and high dissolved oxygen. This is the type behind many sudden pinhole leaks in otherwise sound-looking pipes.

Erosion corrosion

Fast, turbulent water strips the protective film from the inside of the pipe. The NPL describes grooves or “horseshoe” marks, typically downstream of elbows or in hot water return lines. It recommends keeping flow below 2 m/s in cold water and 1.2 m/s in hot water to prevent it. In a home, that is a design and installation matter: pipes that are too small for the flow, or badly fitted bends, make it more likely.

Iron, steel and galvanised pipework

Older iron pipes rust. The DWI notes that iron in water arises from corrosion of iron pipework, and that galvanised pipes and plated taps can leach cadmium. If your home has dark, very hard, sometimes rusty pipes, you are probably looking at iron.

What causes it

The usual suspects, drawn from the DWI, NPL and building services research:

  • Water chemistry. Low pH and low alkalinity make copper and lead dissolve more readily. Hard water can form a protective scale, which is why harder water tends to carry less lead.
  • Dissolved oxygen. In closed heating systems, CIBSE Journal identifies dissolved oxygen as the primary cause of corrosion. It gets in through aerated make-up water, air drawn through valves, or diffusion through plastic pipework that has no oxygen barrier. That is why radiators and boilers can sludge up with rust even when the pipes are fine.
  • Flow rate and turbulence. See erosion corrosion above.
  • Installation. Poor jointing, flux left inside the pipe, mixed metals and sharp bends all raise the risk. The DWI also warns that lead solder, still permitted in closed central heating systems, is sometimes wrongly used on drinking water pipes by unqualified installers.
  • Stagnation. Unused pipe runs, such as a spare bathroom or a property left empty, let water sit and attack the pipe. The NPL recommends regularly flushing unused runs.
  • Mixed metals. Less noble metals such as aluminium, steel and zinc can corrode where they meet other metals, which is one reason connecting different materials needs care.

Scale is a different problem from corrosion, though the two often turn up together in boilers and hot water systems. If you manage a commercial site, this guide on descaling commercial water boilers covers the limescale side.

Signs your pipes are corroding

Look for these, roughly in order of how often people notice them:

Sign What it may mean
Brown or orange water, especially after the taps have been off Rust from iron or steel pipework, or sediment disturbed in the system
Blue or blue-green water or staining Copper dissolving, often linked to soft water or poor installation
Cloudy or milky water Often trapped air, but worth checking if it persists
Low water pressure Internal build-up narrowing the pipe, or a hidden leak
Green or white crusty deposits on joints and fittings Copper or brass corroding at a joint
Stains on floors or carpets, damp or mould on ceilings and walls A leak, possibly from a pinhole
Radiators cold at the bottom, black or brown water when bled Corrosion debris in a heating system

Water UK’s guide to water in your home lists discoloured water, including brown, orange and blue-green, as a sign to look into. Its WaterSafe campaign adds low pressure, rust and water stains on floors, and mould on ceilings and walls as tell-tale signs of leaky plumbing.

A quick way to identify what you have: the DWI describes copper as bright, hard and dull brown, iron as dark, very hard and possibly rusty, and plastic as typically blue, or grey or black if older. Lead is dull grey and soft, and shows shiny silver metal if gently scraped, according to Water UK.

What to do first

The right first move depends on what you see.

Water is leaking now

Turn off the water at the internal stop tap, switch off any electrics near the wet area and open cold taps to drain the system. Then get the pipe made safe. Our emergency callout is available 24/7 across London, and the job is quoted at a fixed price before work starts. If you cannot see where the water is coming from, our leak detection service is built for that problem, and our guide to finding hidden leaks fast explains the usual signs.

Water is leaking now

Blue or blue-green water

Water UK advises that you contact your water company immediately and, if needed, arrange an inspection of your plumbing. Water company advice and a plumbing inspection go hand in hand here: the company can speak to your supply, and an engineer can look at your pipework, joints and fittings.

Brown or orange water

Run the cold tap at the kitchen sink for a few minutes. If it clears quickly, the cause is often disturbed sediment. If it stays discoloured, or comes back repeatedly, ask an engineer to look at the pipework, particularly if your home has older iron or steel pipes.

Possible lead pipes

Water UK says homes built before 1970 may have lead pipes, since use in drinking water became illegal after 1970. The DWI advises asking your water company to test the water at your kitchen tap. In the meantime, Water UK suggests running the tap to clear water that has stood overnight or for several hours, using that water for the garden rather than for drinking or cooking. Lead dissolves into standing water, and the DWI notes more dissolves in summer and autumn. If you are pregnant, have a baby or young children in the house, or are worried about a test result, speak to your GP or health visitor.

If work is done on a lead pipe, the DWI recommends flushing the tap for at least 10 minutes afterwards. Replacing lead pipes as soon as possible is the long-term answer. The water company will replace its own section free of charge if a sample exceeds the legal lead standard, but the pipe inside your property boundary is yours to deal with. The DWI’s 2024 report found 53 lead compliance sample failures out of 13,394 samples, and notes that lead is largely confined within home boundaries, which puts it under the homeowner’s control.

One more point from Water UK: lead pipes may have been used for electrical earthing. Before anyone alters them, you may need advice from your electricity supplier or an approved electrical contractor.

Possible lead pipes

Repair or replace a corroded pipe?

This is the question most people searching “corroded pipe repair” actually have. There is no universal rule, but this is how an engineer thinks about it.

Situation Usual approach
One pinhole in an otherwise sound pipe, accessible Cut out and replace the short affected section, or repair the joint
Corrosion at a single joint or fitting Remake the joint or replace the fitting
Several leaks along the same run Replace the run: more holes are likely to follow
Visible pitting, thinning or green staining along a length Replace that length, and find out why it happened
Lead pipework Replace, rather than repair
Heavily rusted iron or galvanised pipe Replace with modern pipe, particularly if water is discoloured
Heating system sludge Clean the system, then address where the oxygen is getting in

Two principles sit behind the table. First, a repair only holds if you fix the cause. If erosion is stripping the pipe because of tight bends and fast flow, patching one elbow just moves the failure down the line. Second, chemistry is not a substitute for good design. CIBSE Journal argues that chemical inhibitors should be a secondary line of defence, after the oxygen problem is fixed, and that sampling the water alone gives only a snapshot.

We cover the decision in more depth in our guide to pipe replacement in London. If you are weighing up a bigger job, the scope and price are agreed up front: we quote at a fixed price before work starts, and our article on what a fixed price plumber’s quote covers explains what that means in practice.

Corrosion in the heating system

If radiators are cold at the bottom, the boiler is noisy, or black sludge comes out when you bleed a radiator, the problem is likely corrosion debris in the circuit. Oxygen is the driver, so the fix is more than a flush. Our engineers are Gas Safe registered, which matters because any work touching a boiler or gas appliance must be done by a registered engineer. For ageing systems that keep sludging, our boiler installation service and gas works cover the next step. If you have lost hot water altogether, start with what to check and when to call an engineer.

Preventing corrosion

You cannot change your water supply, but you can reduce the risk:

  • Flush unused runs. Run taps and flush toilets in rarely used rooms, and flush the system before a property is reoccupied. The NPL recommends regular flushing to avoid stagnation.
  • Insulate and separate. The NPL advises lagging hot water pipes near cold ones and controlling operating temperatures.
  • Design for flow. Correctly sized pipes and gentle bends keep velocity below the NPL’s limits (2 m/s cold, 1.2 m/s hot).
  • Choose compatible materials. Water UK standards guidance says copper alloy and gunmetal fittings are successfully used with stainless steel tubing in domestic water systems, while less noble metals need care.
  • Keep air out of heating circuits. Fix leaks, bleed radiators properly and have make-up water and air ingress addressed, rather than relying on inhibitor alone.
  • Use qualified installers. Lead solder on drinking water pipework is a known installation error, as the DWI notes. Having the work done properly the first time avoids it.

Landlords and business managers have an extra reason to act early: an undetected leak in a void unit or plant room can cause far more damage than the pipe is worth. Regular checks of exposed pipework, stop taps and tanks cost little compared with a ceiling coming down.

Getting corroded pipes sorted in London

We fix corroded pipework across London, from pinhole leaks and failed joints to replacement runs and heating-system problems. Our engineers are Gas Safe registered, calls are answered 24/7, and every job is quoted at a fixed price before work starts, so you know the cost before anyone picks up a tool. For planned repairs and replacements, see our plumbing work page, and for emergencies use the emergency callout page.

Evoplumbers

If you are not sure how serious the problem is, describe what you are seeing and we will tell you whether it needs an urgent visit or can be booked in. You can also browse our wider plumbing services in London or the Evo Plumbers blog.

Our view on corrosion

Most corrosion calls start the same way: a small stain, a drip, or water that looks wrong, put off for weeks because it seems minor. The pipe does not get better in the meantime.

Our advice is to treat the first sign as information. Find out whether it is one tired joint or a whole run reaching the end of its life, and get that answer while the fix is still small. A fixed price agreed before work starts means you can make that decision without worrying about the bill growing.

We would rather replace the right section once than patch the same pipe three times. That is why our Gas Safe registered engineers look at the cause as well as the leak, and why we are on the phone 24/7 across London when a pipe lets go at night.

the author

FAQ

Is rust-coloured water from the tap dangerous?

Brown or orange water usually means iron from corroding pipework or disturbed sediment. It is a sign the system needs looking at rather than a reason for panic. If it does not clear after running the cold tap, or keeps returning, have an engineer inspect the pipes. If you are unsure about drinking it, speak to your water company.

Does copper pipe corrode?

Yes, but usually only in adverse conditions. The NPL says copper normally gives a long trouble-free life, with problems arising from a combination of materials, design, installation and water quality. When it does fail, it tends to show as pinholes, leaks or blue water.

Can a corroded pipe be repaired, or does it need replacing?

A single pinhole or a failed joint can often be repaired by replacing a short section. If there are several leaks on one run, visible pitting along a length, or the pipe is lead or heavily rusted iron, replacement is usually the better route. An engineer can tell you which applies once they have seen the pipe.

How long does it take for pipes to corrode?

It varies widely. The NPL notes that pitting in copper can appear anywhere from a few months to more than 10 years after installation, depending on water, installation and design. Many copper systems never develop problems.

Who should I call about corrosion in my home?

For leaks, damaged pipework or a heating system affected by rust, call a plumber, and ours are on call 24/7 across London. For blue-green water or a suspected lead pipe, also contact your water company, which can advise on testing and on replacing its own section of pipe.

Sources

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