Guides · Harrow

Who Is Responsible for Your Drain: You or Thames Water?

The most expensive mistake with a blocked drain is paying to fix a pipe that was never yours. In Harrow and across the rest of the London Borough of Harrow, Thames Water is the sewerage undertaker, and a significant proportion of the drainage running under and around your property is legally theirs to maintain - and to unblock, at no cost to you. This page explains where the boundary falls and how to work out which side of it your problem is on before you call anyone out.

What changed in 2011, and why it matters

On 1 October 2011, ownership of most private sewers and lateral drains in England and Wales transferred to the regional water companies. Before that date, homeowners were responsible for shared drainage running under neighbouring properties and out to the public sewer, and disputes between neighbours over who paid were common. After that date, most of it became the water company's. For Harrow, that means Thames Water. A great many homeowners still do not know this transfer happened and pay privately for work that Thames Water would carry out free of charge.

The boundary rule in plain terms

The general test is twofold: where the pipe runs, and how many properties it serves. A drain that sits within your property boundary and serves only your property is yours to maintain. Once that pipe crosses your boundary, it becomes a lateral drain and is generally Thames Water's responsibility, even though it may still be under your neighbour's garden or the pavement. And a pipe that serves more than one property - a shared run collecting from a terrace, for example - is generally a public sewer and Thames Water's, regardless of whose land it crosses.

How to work out which you have

Lift the inspection chamber covers on your property and look at where the water is standing. If the chamber nearest your house is full but the one closest to the boundary is running clear, the blockage is between them and is almost certainly yours. If every chamber on your property is full and backing up, the blockage is downstream of your boundary, which points to a lateral drain or public sewer - Thames Water's problem. A further clue costs nothing: ask your immediate neighbours whether they are having problems too. If several properties are affected simultaneously, it is a shared run, and you should be calling Thames Water rather than a contractor.

What Thames Water will and will not do

Thames Water will attend and clear blockages in public sewers and lateral drains at no charge - there is no call-out fee, because it is covered by your sewerage bill. Harrow Council confirms the position on its own website: Thames Water is the sewerage authority for the borough, and they will check the assets connecting to your property, though not the drainage within it. What they will not do is clear a blockage inside your boundary serving only your property, deal with internal pipework, or take on private systems never connected to the public network such as septic tanks and cesspits. If they investigate and find the blockage is on your private drainage, they will leave it with you rather than clear it, which is why the chamber check above is worth doing first. Blockages are reported through the Thames Water website.

The local complication in Harrow

Much of Harrow and the surrounding area is inter-war and Victorian housing built with shared back-of-plot drainage - a single run collecting from several properties along the rear boundary before joining the public sewer. Streets around Wealdstone, Kenton and South Harrow are laid out this way. Those shared runs are exactly the drainage that transferred to Thames Water in 2011, and they are also where blockages most often appear, because the original clay pipework is now well over eighty years old and prone to root ingress and dropped joints. If your property backs onto others and shares a rear drainage run, there is a reasonable chance the pipe causing your problem is not yours to pay for.

Common questions

How do I find out if my drain is shared?

Lift the chambers and look at the direction of flow and how many inlets each chamber has. A chamber taking pipes in from more than one direction is usually collecting from more than one property. You can also request a sewer map from Thames Water, which shows the public system in your area, or check the drainage and water search from your conveyancing if you still have it.

What if Thames Water say it is my responsibility?

Ask them to record the reason and confirm it in writing. If a private contractor then finds the blockage is in a shared run or beyond your boundary, that evidence - with photographs or CCTV footage - can be put back to Thames Water. A reputable drainage firm will tell you honestly if the problem sits on the public system, because there is no work in it for them either way.

Who is responsible for a blocked drain in a rented property?

Where the drain is the homeowner's responsibility, that generally falls to the landlord under their repairing obligations rather than the tenant, unless the blockage was clearly caused by tenant misuse. Where the drain is Thames Water's, either the tenant or the landlord can report it.