Every time it rains heavily, the internet slows or dies. A few hours after it stops, it recovers on its own. The pattern repeats all through the wet season.
Many people accept it as normal and stop reporting it. Yet this is the most useful pattern you could bring to your provider, because a pattern points to a specific cause.
Fibre and water
There is a common misunderstanding: that fibre is unaffected by rain because it carries light, not electricity.
The first part is true. The optical fibre itself is genuinely unaffected by water. But an internet connection is not only fibre, there are connectors, fusion splices, and splitter terminals on poles or in street cabinets.
Those are the points where water gets in. A flooded or damp connector loses some of the light, and the signal reaching your house weakens below the threshold it needs.
The clue is in the LOS light. If it turns red or blinks during rain and goes out once things dry, there is almost certainly seepage somewhere on the outside route. This is very useful information for a technician, what it means is explained in the guide to router indicator lights.
Telling the cause from the symptom
| Symptom | Most likely cause |
|---|---|
| Dead during rain, recovers once dry | Water in an outside joint or terminal |
| Gradually slower, never fully cut | Damp on a copper joint |
| Dies suddenly and does not recover | Lightning, or a severed cable |
| Stays normal, only Wi-Fi weakens | Not the rain, check inside the house |
| Dies at the same time as the power | A power cut, not a line fault |
The last two rows are often mistaken for rain faults. If Wi-Fi weakens but the connection to the provider is normal, the cause is inside the house, the order to check is in the guide to fixing slow Wi-Fi.
What you can check yourself
Trace the cable from outside to where it enters the house
Look for any section hanging in a dip. Water collects at the lowest point and seeps in from there. The cable should enter with a slight downward loop just before the wall opening, so water drips off before reaching it.
Check the hole through the wall
If the opening where the cable passes is not sealed, water tracks inside along the cable. This is a very common cause and one you can fix entirely yourself.
Look at the terminal box on the outside wall
If there is a junction box outside, make sure its cover is tight and faces downwards. A box with a loose cover collects water every time it rains.
Note the times
Date, time it started, time it recovered. Three or four occurrences is enough to show a pattern that cannot be argued with.
On lightning
Lightning behaves differently from water. It does not need to hit your house, a strike near the cable route can produce a surge that travels inwards.
What fails most often is not the router itself but the network ports on cabled devices, and power adapters.
Sensible protection, in order of effectiveness:
- Unplug during close, loud lightning: from the mains and from the incoming line. This is the only protection that comes close to certain.
- Surge protectors on the sockets feeding network equipment. Cheap, and helpful for surges that are not extreme.
- Proper earthing on the house wiring. This is an electrician's job, but it affects every device, not only the network.
A battery backup often provides surge protection as well, the considerations are in the guide to a UPS for your router.
Reporting it in a way that works
Faults that appear and clear on their own are the ones most often closed without a fix, because by the time a technician arrives everything is normal again.
What changes that is bringing a pattern rather than a complaint:
- A list of dates and times from several occurrences, along with the weather at the time.
- The state of the indicator lights during the fault, the LOS one especially.
- Say that the pattern follows the rain. This steers the response towards inspecting the outside route rather than swapping equipment in the house.
- Ask for a ticket number each time you report, and quote the previous one when it recurs.
If repeated reports still go unaddressed, the escalation ladder and your rights as a customer are covered in the guide to customer rights when the internet is slow.
Getting through the outage
For work that cannot wait, tethering from a phone is the fastest fallback, mobile networks are generally not affected by rain in the same way. How to prepare for it is covered in the guide to Wi-Fi for studying and working from home.
Frequently asked questions
Does rain genuinely affect fibre internet?
The optical fibre itself is unaffected by water, because it carries light rather than electricity. What is affected are the joints, connectors, and terminals outside the house, if there is a gap, water gets in and less light passes through.
Why does the fault only appear a few hours after the rain?
Because water takes time to seep into a joint or terminal. That pattern is actually a useful clue: a delayed fault almost always points to seepage rather than equipment inside the house.
Should the router be unplugged during a thunderstorm?
For close, loud lightning, unplugging from both the mains and the incoming line is the surest protection. Surge protectors help, but guarantee nothing against a direct strike.
How do you report a fault that only appears when it rains?
Collect the dates and times across several occurrences, then present it as a pattern. A report saying "every time after heavy rain" with clear dates is handled differently from an ordinary fault report.
