New research by London Water Services has found that water ingress into copper broadband infrastructure is one of the most under-reported causes of slow speeds and outages in UK homes, and that millions of households on ageing copper connections could be affected without knowing it.
The connection most households miss
Around 22% of UK premises, or approximately 6.6 million homes, are still served by fibre-to-the-cabinet (FTTC) broadband, which uses a copper final mile from the street cabinet to the property. Ofcom’s Connected Nations Spring 2025 report puts the UK’s total premises at 30.2 million, with 74% on full fibre as of January 2025. The remaining quarter are still exposed.
That copper final mile is the network’s most vulnerable point. When moisture seeps into cables, connectors or street cabinets through flooding, ground saturation or damp in the building itself, it corrodes the copper and interferes with the electrical signal that carries broadband data. The result is not always a complete outage. Often it is a persistent, unexplained speed reduction that looks like a provider problem and gets logged as one.
One documented case on BT’s network shows a customer’s speed dropping from 50Mbps to 25Mbps following two water ingress faults. Even after the cable joints were repaired, the speed did not recover because residual moisture had tracked along the cable beyond the repair points.
Most people assume slow broadband is the provider’s fault, but that’s not always the case according to a spokesperson from London Water Services. “Damp walls, leaking pipes and water in plant rooms are just as likely to be the cause, particularly in pre-war buildings still connected via copper.”
The scale of the problem
Water-related broadband faults are not rare. One UK network operator attributed more than 80 telephone and broadband faults per month solely to moisture seeping into the plastic coating of copper cables, causing corrosion that degraded service and in the worst cases caused total failure of both phone and broadband.
At the national level, a Uswitch survey of 2,000 UK adults conducted in November 2025 found that 41% had experienced at least one broadband outage in the past 12 months, with 15 million people reporting outages lasting three hours or more. Weather and infrastructure damage are among the leading causes of faults that exceed standard repair times.
London’s specific exposure
London combines several factors that raise the risk above the national average: a dense stock of pre-war properties where damp is endemic, a high proportion of basement flats with chronic moisture problems, and ageing water mains infrastructure that generates frequent pipe bursts and ground-level leaks. Broadband ducting and water pipes often share the same plant rooms, risers and underground routes.
According to the Environment Agency, 6.3 million properties in England are in areas at risk of flooding. That figure will rise to 1 in 4 properties by mid-century. For households on copper connections in high-risk zones, the overlap between flood risk and broadband vulnerability is direct and growing.
The £9.98-a-day entitlement most customers never claim
Under Ofcom’s automatic compensation scheme, customers whose broadband or landline remains unrepaired after two full working days are entitled to £9.98 per day in automatic compensation without needing to ask for it. A week-long outage from flood-damaged infrastructure would entitle the customer to around £50. In 2024, broadband providers paid £63 million in total compensation across approximately one million incidents.
Crucially, compensation is not limited to complete outages. If the fault results in a loss of service that is then reported to the provider, the clock starts regardless of the underlying cause. Water damage to the network is not excluded from the scheme.
What to do if you suspect water damage
If your broadband speed drops significantly after rain, flooding or a pipe leak in your building, the first step is to report it to your provider as a fault, not a general complaint. This starts the repair clock for automatic compensation purposes. Request that an engineer physically inspects the line rather than running a remote test, which will not detect intermittent moisture-related degradation.
If the fault cannot be resolved on copper and you have access to full fibre, the fastest permanent fix is to migrate. Openreach’s full fibre network carries data as light through glass rather than electrical signals through copper, making it immune to water ingress and corrosion.
