The short answer

Since 1 October 2011, most shared drains and private sewers outside a property boundary have belonged to the water company. Across most of North London, that is Thames Water. A drain that serves only your property, up to your boundary, is still yours. If the blockage, flooding or smell is outside your boundary, report it to Thames Water. If it is inside, you need a drain clearance contractor.

Drain, lateral drain, sewer: what is the difference?

People use these three words as if they mean the same thing. They do not, and the difference decides who you contact because each pipe has a different owner.

Drain: the pipe that carries waste water away from one property.
Lateral drain: the part of that pipe beyond your boundary, which runs on to the public sewer. It often lies under the pavement, drive or front garden.
Sewer: a larger pipe that collects waste water from several properties on its way to treatment.

Before October 2011, many homeowners were responsible for drains and private sewers beyond their boundary. That meant a blockage under a road you did not own could still be your bill. The water company now looks after most of these pipes. Gov.uk and Water UK both describe the change, so check with your water company if you are unsure how it applies to your street.

However, the pipe inside your boundary did not change. Your internal drains, gullies and any pipework that serves only your property remain yours.

The blockage is outside your boundary

Suppose the smell, flooding or slow drainage is clearly beyond your property line. It might surface in the street, or in a shared alley between Victorian terraces. In that case, call Thames Water before you call a drainage contractor. They should investigate, and if the pipe is theirs, they should clear it.

Two things help before you report it, because they speed up the visit. First, work out roughly where the problem is. A road junction, a house number or a description of what you can see helps them find it faster. Second, remember that Thames Water may tell you the pipe sits inside your boundary or serves only your home. If so, you will need a drain contractor instead. Our article on who is responsible for blocked sewage covers the same ground from another angle.

The blockage is inside your boundary

While a problem outside the boundary is the water company’s job, a problem in your garden, drive or under the house is yours to arrange and pay for. An engineer finds the blockage and clears it. The cause is usually fat and grease, tree roots or, in older terraces, a cracked or displaced clay pipe. Rodding or high-pressure jetting normally clears it. Our guide to clearing a blocked drain across North London explains each method.

A CCTV survey tells a blockage apart from a structural fault. That is useful because a structural fault needs a repair, not another clear-out. Our article on what changes the price of a CCTV survey explains what you pay for. Meanwhile, if the survey finds a broken pipe, collapsed drain repair and the no-dig fix explains the options.

Avoid pouring anything caustic down a backed-up drain. It will not reach a blockage that sits further along, and it can harm older clay pipes. For example, strong chemicals can attack old joints. We have no call-out fee, and we agree a fixed price before work starts. You can ask through the online enquiry form.

We work across the area, so for example you can read about drain unblocking in Enfield, blocked drains in Barnet and drain clearance in Edgware. Our blocked drains page lists the full service.

Shared drains and disputed boundaries

The hardest cases are the ones where ownership is not obvious, because the pipes are hidden. A terrace may have one drain that runs under several back gardens and serves three or four homes. Nobody is sure where their part starts or stops.

Talk to the neighbours who share the pipe first. A shared blockage is everyone’s problem. Therefore, splitting the cost of a survey is usually quicker than a stand-off. If that does not settle it, ask Thames Water whether the pipe belongs to them. Your local council’s environmental health team may also be able to help if the households cannot agree.

Keep a written record. Note who you spoke to, what Thames Water said and what any survey found. That makes any later dispute far easier to handle. Because blockages repeat in some areas, why drains block so often in North London is worth reading too.

To tell a branch blockage from a main-run problem, read blocked drain pipe: branch or main run. If you want a guide for the sewer itself, see how to unblock a blocked sewer pipe. Older estates have their own pipe problems, and what clay drains need in Edgware is one example. If you want to avoid repeat trouble, see how often you should have drains cleaned. Finally, our note on why we offer 24-hour emergency drain services explains when a blockage cannot wait.

Frequently asked questions

Who is responsible for a blocked drain outside my house? It depends on where “outside” is, because ownership follows the boundary. A pipe under the pavement or road is probably the water company’s, and Thames Water covers most of North London. A pipe inside your boundary, such as a garden gully or drive drain, stays yours.

Is a blocked shared drain my responsibility? Most shared drains became the water company’s in October 2011, so usually not. However, a drain that was never adopted may stay with the households that use it. In that case, the cost is normally shared between them.

What is the difference between a drain and a sewer? A drain serves one property, while a sewer takes the flow from several. When two or more drains join, the pipe is a sewer. Water companies look after most sewers and many lateral drains.

Does Thames Water charge for clearing a blocked lateral drain? If the pipe is theirs, they clear it without billing the homeowner, since it is their asset. You pay only for work on pipework inside your own boundary. Ask Thames Water to confirm which side of the line the blockage is on.