Blocked drain: you or Thames Water

When a drain blocks, the first question is usually who pays. In London the answer changed in 2011, and many people still do not know it. A lot of blocked drains that homeowners pay to have cleared are actually Thames Water’s responsibility.

What changed in 2011

Before October 2011, homeowners were usually responsible for the shared drains and private sewers behind and under their homes, even where they served a whole terrace. On 1 October 2011, the law transferred most of these pipes to the water companies. In London, that means Thames Water.

Thames Water says it became responsible for private sewers and drains from that date. You are still responsible for the section of pipe between your property or building and the transferred sewer or lateral drain, plus all your internal plumbing.

A simple way to picture it

Pipe	Who usually looks after it
Waste pipes inside your home	You, or your landlord if you rent
Drain serving only your property, inside your boundary	You
Drain shared with neighbours	Thames Water, since 2011
Lateral drain, your pipe once it runs outside your boundary	Thames Water, since 2011
Public sewer under the road	Thames Water
Drains serving a block of flats, inside the site	Often the freeholder, check the lease

The neighbour test

Thames Water’s own advice is to work out where the problem is before you call anyone. The steps are simple.

1. Ask your neighbours if their drains are slow or blocked.
2. If they are fine, the blockage is probably in your section of pipe and you will need to deal with it yourself.
3. If they have the same problem, it may be in a shared section that Thames Water looks after.

You can also lift the inspection chamber cover nearest your house if you can do it safely. If the chamber is full of water, the blockage is further down the line, possibly in a shared section. If it is empty while your gully or sink is backing up, the blockage is between your house and that chamber, which is usually yours.

Thames Water notes that it may charge for unnecessary callouts, so the neighbour test is worth doing.

Lambeth terraces and shared runs

In Lambeth, many Victorian terraces in Brixton, Stockwell and Clapham have drain runs that go under several back gardens before reaching the sewer in the street. In the 2021 Census, 15.0% of Lambeth households lived in terraced houses and 20.6% in converted houses (Nomis, TS044). That is a lot of homes on shared runs.

When a shared run blocks, the house at the lowest point floods first. That household may have caused none of it. Since 2011, a blockage in that shared section is generally Thames Water’s to clear.

Flats and the freeholder

Flats add another layer. In a house split into three flats, the internal waste pipes and the soil stack serve all three. The Leasehold Advisory Service says the freeholder is usually responsible for communal pipes that serve more than one flat. So a blocked stack or a blocked drain under the building is often a matter for the managing agent, not one flat.

Once the drain from the building leaves the boundary and joins neighbours’ pipes or runs under the pavement, the 2011 transfer may apply and it becomes Thames Water’s.

What to do when the drain is blocked

1. Stop using water in the property, including the washing machine and dishwasher.
2. Do the neighbour test.
3. Look in the nearest chamber if you can lift the cover safely.
4. If it looks shared, report it to Thames Water through its report a problem page or on 0800 316 9800.
5. If it looks like yours, call a plumber or drainage engineer. Our blocked drains page explains what the visit involves.
6. If you rent, tell your landlord in writing.

When it is sewage inside

If sewage is coming up inside the home, through a toilet, shower or floor gully, treat it as an emergency. Keep away from the water, switch off electrics in the area if it is safe, and stop using water. If it only happens in heavy rain, the sewer may be overloaded rather than blocked. Thames Water has a sewer flooding service for that. Our guide to basement flat flooding covers it in more detail.

Keep a record

Whoever ends up clearing the drain, note the date, take photos of the full chamber and any flooding, and keep a copy of any report you make to Thames Water or the managing agent. If the same drain keeps blocking, those records help show it is a shared or structural problem rather than something one household keeps causing. A camera survey can show cracks, roots or a sagging pipe, and tell you whose section it is on.

Keeping shared drains clear

The same few things block most London drains: cooking fat that sets in the pipe, wet wipes and food waste. On a shared run, everyone’s habits affect everyone else. A quick word with the neighbours costs nothing and saves the lowest house a flood.