Thames Water Leak Allowance: What to Do When You Find a Leak

What Is the Thames Water Leak Allowance?

The Thames Water leak allowance is a scheme that allows metered customers to apply for a reduction in their water bill where a significant increase in metered consumption has been caused by an undetected leak in the supply pipework between the water meter and the property. Thames Water recognises that some leaks, particularly those in underground supply pipes or in concealed pipework within walls and floors, can run for weeks or months before being detected, generating a water bill that is entirely disproportionate to the household actual consumption.

The scheme allows metered customers to apply for a one-off allowance that reduces the abnormally high bill to a level closer to the household normal consumption. Thames Water will typically allow the equivalent of one abnormal billing period, meaning that if the leak ran for six months before being detected, Thames Water may credit back approximately three months worth of the excess consumption. The exact terms of the allowance vary and Thames Water updates its policy periodically, so it is important to check the current scheme details on the Thames Water website when making a claim.

Who Is Responsible for Leaks in London Supply Pipework?

The responsibility for water supply pipework in London is split between Thames Water and the property owner at the boundary of the property, which is typically the external edge of the building or the property boundary line. Thames Water is responsible for the supply main in the street and the pipe from the street main to the boundary stopcock, which is usually located in the footpath just outside the property boundary. The property owner is responsible for the section of pipe from the boundary stopcock through to all internal outlets.

A leak in the external section of the supply pipe, from the street main to the boundary stopcock, is Thames Water responsibility to repair. A leak in the internal section, from the boundary stopcock to any internal outlet, is the property owner responsibility. If you notice a wet patch in the front garden, a persistently damp area of the footpath, or unexplained water appearing at the boundary of your property, this may indicate a leak in the section of pipe that is Thames Water responsibility, and you should report it to Thames Water immediately.

How to Detect a Leak in a London Property Using the Water Meter

The most reliable method for detecting a hidden leak in a London property supply pipe is to use the water meter. The procedure is as follows: ensure that all water outlets in the property are turned off, including any ice makers, washing machines on standby, and automatic irrigation systems. Locate the water meter, which in most London properties is in a small underground chamber in the footpath outside the front of the property, and note the current reading. Wait for a period of thirty minutes to one hour during which no water is used, then return to the meter and check whether the reading has advanced. If the meter has moved during this period, water is flowing through the meter without any outlet being open, which indicates a leak in the supply pipework between the meter and the outlets.

A rough calculation of the leak rate can be made from the meter reading: most Thames Water meters measure in cubic metres, so a movement of 0.01 cubic metres (10 litres) over 30 minutes indicates a leak rate of approximately 20 litres per hour, or 480 litres per day. At current metered rates, this represents a cost of approximately forty to fifty pounds per month in wasted water, and after repair the Thames Water leak allowance could provide a credit for a portion of the excess charges incurred while the leak was running.

Tracing and Repairing a Leak in London Supply Pipework

Once a leak has been detected using the meter test, the next step is to identify the location of the leak so that targeted repair can be carried out. Visual inspection of the front garden, cellar, and under-floor spaces may reveal obvious signs of water ingress. For leaks in underground or concealed pipework, acoustic leak detection equipment is required. Acoustic detectors amplify the sound of water escaping from a pressurised pipe and allow the engineer to pinpoint the leak location to within a few centimetres without excavation.

Prestige Engineers carry acoustic leak detection equipment on all vans and can carry out leak investigations across London as an emergency or scheduled appointment. Once the leak is located, the repair may involve excavating a section of front garden or driveway to access and repair the underground supply pipe, or making an access opening in a floor or wall to repair concealed internal pipework. After repair, a further meter test confirms that the leak has been fully resolved before the Thames Water leak allowance application is submitted.

How to Apply for the Thames Water Leak Allowance

To apply for the Thames Water leak allowance after a leak has been repaired, the customer must provide evidence that the leak has been repaired and that the current water consumption has returned to normal levels. Thames Water requires a receipt or invoice from a qualified plumber confirming the nature of the repair and the date it was carried out, together with a completed leak allowance application form, which is available on the Thames Water website or by telephone.

Thames Water will review the application and compare the metered consumption during the period of the leak with the household normal consumption before and after the leak. A credit will be applied to the account reflecting the proportion of the excess consumption that Thames Water agrees to write off. Processing times vary but are typically four to eight weeks. Prestige Engineers can provide a full repair invoice and any supporting documentation required for the Thames Water leak allowance application as part of the leak repair service.