Thames Water says you have a leak: the four week rule explained

A letter or email from Thames Water saying it has detected a leak at your property can come out of nowhere. You may not see any water at all. The leak might be under your front path, under the floor or in a toilet that runs constantly into the pan. Whatever it is, the clock has started, and it helps to know what the rules actually say.

The four week rule

Thames Water’s leaks at home guide is direct about it. Whether you find a leak or Thames Water confirms one at your property, you must fix it within four weeks. Once it is fixed, you tell Thames Water so it can update its records.

There is an upside to acting quickly. If you arrange the repair within four weeks, you may be eligible to claim the cost of the water lost. If you are on a meter, Thames Water compares your past use with the amount recorded while you had the leak. If you are not on a meter, it bases the allowance on typical use for a similar household. Terms and conditions apply.

If you do not fix the leak within four weeks, Thames Water says it will step in. Under Section 75 of the Water Industry Act 1991, it will carry out the repair and charge you for it. In an emergency it may turn off your supply until the leak is repaired.

Which pipes are yours

Pipe	Who is responsible
Water main under the road	Thames Water
Communication pipe from the main to your boundary	Thames Water
Supply pipe from your boundary into the home	You, the homeowner
Shared supply pipe serving several homes	The households served, jointly
Internal pipes, taps, toilets, tanks and appliances	You, the homeowner
Any of the above if you rent	Your landlord

That comes from Thames Water’s pipe responsibility page. It also says you are still responsible for a leak on your supply pipe if the pipe crosses land belonging to someone else, such as a neighbour’s garden or the road.

Why Greenwich homes get these letters

Greenwich has more houses than most inner London boroughs. In the 2021 Census, 26.7% of Greenwich households lived in terraced houses and 21.7% in detached or semi detached houses. Only 6.0% were in converted houses. That means a lot of homes with their own front gardens, their own supply pipes and their own meters.

In older streets in Charlton and East Greenwich, supply pipes can be decades old, some still lead. Thames Water says homes built before 1970 may have lead pipes. Old pipes and their joints can develop slow leaks underground that never show on the surface, because the water drains away into the soil. The first anyone knows about it is a meter reading or a letter.

Finding the leak

Before you call anyone, a few checks help narrow it down.

1. Turn everything off. Make sure no taps, toilets, washing machines or dishwashers are running.
2. Read the meter. Note the reading, wait half an hour without using any water, then read it again. If it has moved, water is escaping somewhere.
3. Close the inside stop tap and read again. If the meter still moves with the inside stop tap shut, the leak is probably on the supply pipe between the meter and the house.
4. Check the toilets. A cistern that keeps running into the pan wastes a lot of water and is easy to miss. Our guide on a toilet that keeps running explains why this is so common in London.
5. Look for signs outside. A soft or wet patch in the garden, water between paving slabs, or one area of grass greener than the rest in dry weather.

A plumber can then confirm where the leak is and repair it. For a supply pipe, that usually means digging down to the pipe and replacing the damaged section, or the whole run if it is old.

Using an approved plumber

Thames Water recommends using an approved plumber or leak detection specialist, or arranging the repair through your home insurance if you are covered. It also says that if you did not use a plumber on the WaterSafe scheme, it may come out to check the work, and will carry out and charge you for extra repairs if it thinks they are needed. It is worth asking any plumber you use whether they are on the WaterSafe register, and checking it yourself.

Shared supply pipes

In older terraced streets, a single supply pipe can serve several houses. Thames Water says this is more common where buildings are close together, and that the households served have joint responsibility for the shared part and the costs. It does not get involved in disputes between neighbours.

If your letter relates to a shared pipe, speak to your neighbours straight away. Agree who will arrange the plumber and how the cost will be split. Four weeks goes quickly when three households need to agree.

After the repair

Once the leak is fixed, tell Thames Water using its online form so it can confirm the repair happened within four weeks. Then claim the leak allowance if you are eligible. Keep the plumber’s invoice and a note of what was repaired and where.

If the leak was on a burst pipe inside the home rather than underground, check for damage to floors and ceilings too. Water that has been escaping for weeks can rot timber and cause mould even after the pipe is fixed.

If you think the letter is wrong

Sometimes a high reading has another explanation, such as a faulty meter or a meter read for the wrong property. If your checks show no movement on the meter with everything off, contact Thames Water, explain what you did and ask how it detected the leak. Keep a note of your readings, with dates and times, and of who you spoke to.