Possible causes of a leaking water pipe

Corrosion and deterioration

The Drinking Water Inspectorate explains that corrosion of pipes and fittings can lead to leaks and structural failure. The process depends on the material and water conditions; age alone does not show how much usable life a particular pipe has left.

If corrosion is found, ask whether the damage is localised or whether nearby pipework also needs assessment. Repeated repairs in the same area justify looking beyond the latest opening rather than assuming each leak is unrelated.

A failed joint, fitting or seal

Connections are another place to investigate. A leak at a joint may require attention to the fitting, seal or connected pipe rather than replacement of an entire pipe run. The repair depends on the connection type and what has failed.

Do not tighten every nearby fitting in an attempt to stop the drip. Identify the source first and avoid disturbing other connections. Tell the plumber if the leak started after an appliance was moved, a valve was operated or plumbing work was completed.

Freezing and thawing

The Met Office warns that freezing and thawing can cause pipes to burst. Pipework in exposed or unheated areas deserves attention during cold weather, including where protection is missing or damaged.

If a leak follows a freeze, mention that history when arranging help. Do not use a flame to thaw pipework. Our guide to preventing winter pipe bursts covers the seasonal precautions in more detail.

Accidental damage during work

If leaking begins after drilling, fixing flooring or building alterations, give the plumber the location and timing of that work. A concealed pipe may have been affected, but the coincidence needs investigating rather than being treated as proof.

Avoid further drilling or opening finishes blindly. For water-based underfloor heating specifically, see causes of underfloor heating pipe leaks, which covers that separate system.

Movement or strain at a connection

A fitting under strain or pipework that has been disturbed may need assessment of its support and alignment as well as the leaking point. Ask whether the proposed repair addresses the reason the connection failed.

Where pressure or movement is suspected, it should be assessed rather than guessed from a strong-looking tap flow. Do not alter pressure controls without identifying the system and the appropriate settings.

Does London’s hard water cause pipes to leak?

Do not assume that hardness explains a particular leak. The Drinking Water Inspectorate distinguishes scale formation from corrosion and notes that local water hardness varies. Your water supplier can provide information for the actual supply.

Hard water can cause scale in hot-water systems and appliances, but a scale deposit does not identify why a joint or pipe has failed. Corrosion involves material and water-chemistry factors that cannot be established from the postcode alone.

Repair the confirmed fault and assess any separate water-treatment question on its own merits. For the heating-appliance issue, our article on limescale and boilers provides a more specific explanation.

What observations help identify the cause?

You can collect useful information without dismantling plumbing. Record:

• The first place you noticed water and whether a source is visible.
• Whether the leak is continuous or appears during use of a tap, appliance or toilet.
• Recent plumbing, decorating or building work nearby.
• Any preceding freezing weather or period when the property was unheated.
• Previous repairs in the same area.
• Whether the water is spreading or affecting another room or property.

A photograph can help describe an accessible leak. Avoid opening a ceiling, lifting floors or removing boxing simply to obtain a better picture.

If water appears around a toilet, distinguish the supply and connections from the ceramic fixture. Our guide to toilet repair or replacement covers that component-level decision.

Does the problem need repair or hidden-leak investigation?

A visible, identified fault: a plumber can assess the damaged pipe, joint or valve and choose an appropriate repair. Our plumbing repairs service covers faults in existing plumbing in London.

Water damage with no confirmed source: investigation should establish where the water is coming from before repair work is chosen. For suspected concealed water leaks, our leak detection service is the relevant next step. A damp patch alone should not be treated as proof of a particular pipe fault.

Rapid or uncontrolled water escape: prioritise limiting damage and getting urgent help. Our article on what counts as a plumbing emergency explains that separate urgency decision.

How can you reduce the chance of the leak returning?

Ask what caused the failure and whether the repair addresses it. Depending on the findings, that may involve replacing a damaged section, correcting a connection or improving protection of exposed pipework.

Keep records of repairs and concealed pipe routes, share them before future building work, and deal with recurring drips promptly. The Met Office recommends insulating vulnerable pipes and knowing where to shut off the water before freezing weather causes a problem.

For a known leak, our guide to dealing with a leaking pipe at home covers the practical next question. The aim is to resolve the cause, not leave a temporary measure in place indefinitely.