Blocked Drain: Is It Thames Water's Job or Yours?

Updated July 2026 · Emergency Plumber Chelsea

The rules changed on 1 October 2011, when most private sewers and lateral drains in England were transferred to the water companies. Since then, in Chelsea and the rest of the Thames Water area, the split works like this. A drain that serves only your property and runs within your boundary is a private drain, and it is yours. The section of that same drain that runs beyond your boundary, usually under the pavement or road to reach the sewer, is a lateral drain, and Thames Water maintains it. A drain that carries waste from two or more properties is a shared sewer, and Thames Water maintains it even where it runs under your garden or back yard. The main sewer in the street is theirs too. Our RBKC drainage and flooding guide covers how this fits with the council's own responsibilities.

Road gullies are a separate case. The grated drains in the kerb that take rainwater off the road belong to the highway authority, which in Chelsea is the Royal Borough of Kensington and Chelsea, so a blocked road gully or a flooded street after rain is reported to the council rather than to Thames Water or a plumber. The gully in your own front area, lightwell or back yard is part of your private drainage, even though it looks similar.

Your inspection chambers give you the best evidence. Most Chelsea houses have one or more covers in the front area, the back yard or a side passage, and the last one before the boundary is often the key one. Lift the covers carefully with gloves on, since old cast iron lids can be heavy or seized, and look at the water level in each. If the chamber nearest the house is full and the next one along is empty or flowing, the blockage is in the pipe between them, which is almost always your private drain. If every chamber on your property is full, including the last one before the boundary, the blockage is probably further on, in the lateral drain or the sewer. Never climb into a chamber, and keep children and pets away from an open cover.

Next, find out whether anyone else is affected. Knock on the neighbours' doors or ask the porter. If the house next door, or several flats in your terrace, also have slow toilets, gurgling sinks or water standing in their chambers, the fault is almost certainly on a shared sewer, and that is Thames Water's to clear. If you are the only one with a problem, the blockage is more likely on the part that only serves you, although it can still be on your lateral drain outside the boundary. Our guide to gurgling toilets and drains explains the early warning signs that often come before a full blockage.

Check which way your drains actually run before you decide. In Chelsea's terraces it is common for several houses to share a single run at the back that crosses a number of gardens before it reaches the sewer, and the owners often do not know it is there. Thames Water publishes sewer records, and a drainage search or a property search from when you bought will often show whether the pipes under your land are public or private. If there is no record and the layout is unclear, a CCTV drain survey shows the route, where the drains join and exactly where the blockage sits, which is the evidence both Thames Water and an insurer will want.

If the evidence points to the sewer, report it to Thames Water rather than paying for it to be cleared. You can report a blocked drain or sewer through the Thames Water website or by phone, and they will send someone to investigate. Tell them the address, whether sewage is coming into the property, whether neighbours are affected, and what you saw in the chambers. Take photos of any flooded chamber and any damage before you replace the covers. If sewage is flooding inside your home, say so clearly, because internal sewer flooding is treated as more urgent than a slow drain. Our guide to sewage coming up through a drain or toilet covers what to do while you wait.

Be ready for the answer to come back the other way. If Thames Water's team finds that the blockage is in your private drain, they will usually tell you it is your responsibility and leave it for you to arrange a contractor. Some water companies offer to clear private drains for a fee, so ask before you agree to anything. If you are confident the blockage is theirs and they disagree, ask them to show you where it is, or get a CCTV survey that locates it. A survey report with the distance from a known chamber settles most disputes quickly.

If the blockage is on your private drain, it will not clear itself, and every flush adds to the problem. Stop using the toilets, sinks and appliances that feed that drain, and do not keep flushing to try to push it through. Clearing the gully grid of leaves and silt is safe to try, and our guide to a blocked outside drain walks through rodding safely. Anything that does not shift with rods needs a professional. Our drain unblocking service uses rods and high-pressure jetting, and our blocked manhole service clears flooded inspection chambers and checks the benching so they do not silt up again.

Flats and mansion blocks add another layer. In most Chelsea blocks and converted houses, the soil stacks and the drains within the building's own land are the freeholder's to maintain, usually through the managing agent, and the cost is recovered through the service charge under the lease. Once the drains leave the block's boundary, or join drains from neighbouring buildings, they usually become Thames Water's. So if you live in a flat, your first call for a blocked communal drain is normally the porter or managing agent, not a plumber and not Thames Water. The exception is the waste pipe that serves only your flat, from your fittings to where it joins the shared stack, which is often your own responsibility under the lease. If the blockage is in a rented home, our guide on whether the tenant or landlord pays for plumbing repairs explains who normally covers it.

A drain that keeps blocking is usually telling you something about the pipe. Many private drains in Chelsea are original Victorian clay, and cracked joints, root ingress and sagging sections trap waste that would otherwise flow. If the same drain blocks every few months, a survey will show whether it needs a repair or lining rather than another clearance. Our guide to collapsed drain repair costs explains what those repairs involve. Some home insurance policies cover accidental damage to underground drains, so check your policy wording before you commit to major work.

Treat it as an emergency if sewage is coming up into the property, if a basement or lower-ground floor is flooding, if you have only one toilet and it is unusable, or if waste is backing up into more than one flat. Stop using water, keep people away from contaminated areas, and report it to the right party straight away. If it is a shared sewer, report it to Thames Water. If it is your private drain, or you cannot tell and need it cleared now, call us. Our emergency drainage service covers out-of-hours blockages across Chelsea.

Emergency Plumber Chelsea clears blocked private drains, gullies and inspection chambers across Chelsea, Knightsbridge, South Kensington, Sloane Square and Fulham. We check where the blockage sits before any work starts, and if it turns out to be on the shared sewer or the lateral drain, we tell you so you can report it to Thames Water instead of paying for work that is not yours. We explain the options and the price up front, and there is no call-out fee on jobs over 3 hours. Call 020 3002 6667.

Quick tips

• Lift your inspection chamber covers. A full chamber near the house with an empty one downstream points to your private drain.
• Ask the neighbours. If several homes are affected at once, the blockage is almost certainly on a shared sewer that Thames Water clears.
• Report blocked road gullies to RBKC, not Thames Water. The gully in your own front area or yard is your drain.
• In a mansion block, call the porter or managing agent first. Communal drains within the block are normally the freeholder's.
• Photograph flooded chambers and any damage before replacing the covers. It helps with reports, disputes and insurance claims.

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