The essentials in 30 seconds
A blocked outside drain shows as water or waste that is slow to drain or not draining, backing up or overfilling, a bad smell or gurgling, Wessex Water says. First work out where the blockage is, because that decides who clears it. If your neighbours have the same problem, or the problem is outside your property boundary, it is most likely the public sewer: report it to your water company, which clears its own pipes for free. If only your home is affected, your property doesn't share a drain and there is no other flooding nearby, the blockage is probably in your private drain, which you are responsible for: Thames Water and Wessex Water point you to a plumber or drainage contractor, and some home insurance includes drainage cover. Tenants should contact their landlord.
- If you can't tell where it is, contact the water company; it will check and tell you.
- Never try to unblock a sewer yourself, Yorkshire Water warns.
Signs of a blocked outside drain
- Water or waste that is slow to drain or not draining.
- Water or waste backing up or overfilling, for example at an outside gully or inspection chamber.
- A bad smell from the drains.
- Gurgling sounds from the plumbing.
- In the worst case, raw sewage coming back into the home.
These are the signs Wessex Water lists. Thames Water adds a toilet that is hard to flush and a sink or bath that empties very slowly.
Your drain or the public sewer?
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01
Ask the neighbours
If they have a similar problem, the blockage is most likely on the public sewer network (Wessex Water, Yorkshire Water).
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02
Compare upstairs and downstairs
If downstairs drains fine but upstairs doesn't, the blockage is most likely in your own pipework (Wessex Water, Thames Water).
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03
Compare rooms
If only one room is affected, the blockage is almost certainly in the pipes on your property (Yorkshire Water).
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04
Look at the access point
If the drain or sewer access point is clear, Thames Water says the blockage is likely within your home.
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05
Shared or not
Check whether your drain joins your neighbours' before reaching the sewer; shared sections are usually not yours alone.
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06
Still unsure
Contact the water company; United Utilities has an online tool, and Thames Water's engineer will tell you if the blockage turns out to be on your section.
Who is responsible for an outside drain in the UK?
| Pipe | What it is | Who clears it |
|---|---|---|
| Private drain | Serves only your property and is within your boundary | The occupier clears a blockage; the owner repairs a defect |
| Lateral drain | Your drain's section outside your boundary, under the road, footpath or someone else's land, before it joins a public sewer | The water company (Thames Water in its area), free |
| Shared sewer | Where your drain joins your neighbours', even under your garden or driveway | The water company, if it connects to a public sewer |
| Public sewer | Under roads and footpaths, serving several properties | The water company, free |
| Private sewer | Serves several properties but doesn't connect to a public sewer (e.g. ends at a treatment plant) | Shared by the households upstream of the blockage |
Thames Water says you are responsible for all waste drainage pipes (such as gullies, gutters and drains) within your property boundary, as long as they serve only your property. Reigate & Banstead Council adds that drainage law covers both foul and surface water pipes, and that foul waste includes sinks, basins, baths, showers, dishwashers and washing machines, not only toilets. Responsibility in flats and shared drains can be complicated; ask the water company. These are UK rules; in the US, check with your city or sewer utility who owns the line from the house to the main.
Getting it cleared
- Public sewer or lateral drain: report it to the water company. United Utilities and Wessex Water clear blockages on their own network for free, and United Utilities says it will try to find the cause.
- Your private drain: contact a plumber or a qualified drainage contractor. Check first whether your home insurance or a separate policy covers drainage; your insurer can advise on a claim.
- Newer homes: if your home is under 10 years old, Yorkshire Water suggests contacting the developer, as the drainage may be under warranty.
- Renting: contact your landlord. Reigate & Banstead notes that a structurally defective private drain is for the freeholder or homeowner to repair.
- If the water company finds it is yours: Thames Water's engineer will discuss it with you; United Utilities can't clear private drains but will try to advise.
This guide doesn't give a rodding method: the water companies cited send private blockages to a drainage contractor. If you only need to clear an indoor fitting, see how to unblock a sink.
Stop it happening again
- Flush only the three Ps: pee, poo and toilet paper. Wet wipes, even those labelled flushable, block pipes, Thames Water says.
- Let cooking oil, fat and food cool and put them in the bin, not down the sink.
- Wrap sanitary items, nappies and wipes and bin them.
- Take chemicals, solvents, engine oil and paint to the local recycling site.
- Yorkshire Water also lists tree roots, heavy rainfall and a collapsed sewer among causes of sewer floods.
Blocked outside drain pipe: FAQs
Who is responsible for a blocked drain outside my house?
In the UK, you are responsible for drains within your property boundary that serve only your home; the water company is responsible for public sewers, lateral drains and pipes shared with neighbours.
Will the water company unblock my outside drain for free?
Yes if the blockage is in its pipework, according to United Utilities and Wessex Water. If it is in your private drain, you pay a plumber or drainage contractor.
How do I know if the blockage is mine?
Only your home affected, a drain not shared with others and no flooding nearby suggest your private drain; neighbours affected or a problem outside your boundary suggest the public sewer.
Can I unblock a sewer myself?
No. Yorkshire Water says never to attempt it, as it puts you at risk and can make things worse.
Does home insurance cover blocked drains?
Some home insurance or home protection policies include drainage cover; check your policy or ask your insurer.
Sources
Water company and council guidance, checked on 2 November 2026 (02/11/2026).
- Thames Water · Blockages and blocked drains ↗Signs; how to tell if the blockage is in your home (neighbours, shared drain, local flooding, upstairs versus downstairs, clear access point); owner versus Thames Water responsibility; plumber and insurance; engineer will discuss if on your section; three Ps, wipes, fat. Read.
- Thames Water · Sewer pipe responsibility ↗Homeowner responsible for gullies, gutters and drains within the boundary serving only the property; water company owns public sewers and sewers shared with neighbours, even under gardens or driveways. Read.
- United Utilities · Blocked drains ↗Hard to know where the blockage is; online tool; clears its own pipework free and investigates the cause; can't clear private drains but will advise. Read.
- Wessex Water · Blocked drains ↗Signs (slow, backing up, smell, gurgling, sewage); neighbours means public sewer; upstairs versus downstairs; private blockages to a qualified drainage contractor; clears its network free. Read.
- Yorkshire Water · Sewer flooding ↗Never unblock a sewer yourself; safety (children and pets, gloves, hands, moved manhole covers); neighbours versus one room; landlord; insurance; developer warranty under 10 years; drainage contractor; causes. Read.
- Reigate & Banstead Council · Blocked drains ↗Foul and surface water pipes; private drain (occupier clears, owner repairs defects); lateral drain cleared by Thames Water free; public sewer; private sewer shared upstream; definitions. Read.
Not sure whose pipe it is?
Ask the neighbours, compare upstairs and downstairs, and call the water company if in doubt: it clears its own pipes for free.