Detecting leaks in mains water supply pipes

A higher than expected bill from your water supply company is sometimes a good indication of a leak, however, there could be a number of other reasons too.

This article covers:

  • Reasons why your water bill could be higher than usual
  • Who’s responsible for fixing a leak in your mains supply
  • What to do if you can’t find your mains water external stop valve
  • How to test for a leak on your exterior water supply pipe
  • Pinpointing the exact location of a leak in buried pipework (without digging!)
  • Exposing a leak, repairing it and submitting an insurance claim


water leak detection

Why do I have a high water bill?

There are many reasons why your water bill could appear higher than you expect. If you have a water meter, ask yourself the following questions. This could save the effort of arranging for someone to come and investigate a potential leak.

Check the information on your water bill

Do the dates cover the same period as your previous water bills?
It’s possible your water supply company has increased the period of time your bill covers compared with previous ones. Subsequently, this would increase the amount of water used for the billing cycle.

Has your high water bill previously been calculated using estimated readings?
Water use that was previously under-estimated would produce a change from the previous bill. The difference between the estimated reading and the current reading would make your bill higher than expected.

What has changed to impact the amount of water being used?

Has any maintenance work been done recently?
Decorating, building and gardening can all significantly increase the amount of water used in the household.

Is there any indication that taps or appliances are faulty?
Something as simple as a dripping tap can increase water bills. Leaking dishwashers or washing machines will also waste water.

Has the number of people using water in the property increased?
People who are less economical with their use of water could be the reason for a larger bill.

If you don’t have a meter, your bills are based on your water supply company’s assessment of the property. This is usually based on the number of bedrooms in the property. In theory this relates to the number of people using water. You can check with your water company their assessed charge is correct. For example, the water being used in a large house could be overestimated if only one person is living there.

You can ask your water supply company to fit a meter, and there shouldn’t be a charge to have it fitted. It’s not always possible to have this done immediately, so it may take some time before fitting it can be scheduled.

If there’s no obvious reason why your water bill is higher than usual it, leak investigation should be the next step.

Will my water company find and fix a mains supply leak?

Properties supplied with water must have an external stop valve. This valve controls the supply of water to that property. When a property contains more than one building, there is usually a single stop valve or multiple external stop valves to control the water. However, each building will have its own meter.

Water companies usually install a meter on the stop valve. When they’re inside communal blocks, they’re located away from the stop valve. Only the water passing through the meter is billable to the customer.

There are two sides to an external stop valve: property side, and street side. Property owners are responsible for any leaks on the property side (even if the meter is inside the property). Water supply companies are responsible for the street side. Water leaking from mains supply pipework on the street side won’t pass your meter. This means that a leak there wouldn’t be the cause of a high water bill.

Please note:

The external stop valve is not the same as an internal stopcock (also called a stop tap). An external stop valve will be outside the property, usually under the pavement or the front garden. A stopcock controls the water supply inside a property. A stopcock is usually located beneath a kitchen sink.

What should I do if I can’t find my external stop valve?

If you can’t find your external stop valve contact your water supply company. They’ll be able to tell you where it is. If you can’t find it you should ask your water supply company to send someone. They’ll show you where it is.

The Water Supply Regulations 1999 state:

“Every supply and distributing pipe providing water to premises should be fitted with a stop valve to control the supply to those premises only.”

If you don’t have an external stop valve, your water supply company would have to arrange for one to be installed.

Locating a leak on mains supply pipework

If you think there is a leak on a main water supply pipe, there’s a simple test to confirm whether it’s inside or outside of the property.

First, turn off the stopcock inside your property. Make sure it’s completely off by turning on a sink tap to drain the system. Water should stop coming out from the tap if the stopcock has been fully turned off.

Second, go to your water meter and make a note of the reading. If the reading increases, it indicates a leak on the mains supply pipework into the property. This means that water is passing the meter but is not going past the internal stopcock.

If it’s a small leak it might take some time for the reading to increase. Keep your stopcock turned off and take a reading after a few hours, or as long as possible.

No water meter?

If you don’t have a meter on your external stop valve you might need some professional help. A pressure test on the pipe between the external stop valve and internal stopcock will show whether a leak is present. Both the external stop valve and the internal stopcock are turned off so water is held between them. If there’s a leak the water pressure will drop.

If the test fails to show a leak is present on the main water supply pipework, the next step is to investigate a leak on pipework within the property.

Read more about investigating a leak on internal pipework here.

Simple tip:

If you’re unsure where your internal stopcock is you should make a point of finding it. Being able to turn your water off could help prevent severe water damage in the case of a burst pipe or plumbing leak. Finally, check you’re able turn the stopcock off and on again without too much difficulty.

How can I find the exact location of a main water leak?

The good news is that if there’s an indication of a leak the exact location can be found with the right equipment. The traditional approach would’ve been to dig a trench to expose the pipe. Digging would continue without knowing where the leak is. This process could be time consuming, and costly, with no knowledge of where the leak might be.

Fortunately, modern technology provides a better way of finding a leak. A buried leak, sometimes referred to as a slab leak, can be located to within a few centimetres by using sensitive acoustic equipment. Once it’s found, the leak is exposed by digging a trench in the exact position it’s needed.

Even if a leak is buried beneath paving slabs, several feet concrete or soil, it can still be found using the acoustic equipment.

The equipment works by placing a highly sensitive microphone on the ground. Tiny vibrations, created as water escapes under pressure from the pipe, are amplified as sound. Then, as the microphone moves over the ground, any changes in sound allows the position of the leak to be pinpointed.

Like all the other non-invasive leak detection methods we use, the acoustic equipment means leaks can both be found more accurately, and fixed more quickly. Another benefit of this approach is that it reduces the amount of reinstatement work needed. The “trace and access” approach we use for detecting leaks is usually required by insurance companies when a claim is being made.

Repairing a damaged mains water supply pipe

When the investigation work is complete and the leak is exposed, a fixed price quote to carry out the repair work can be provided.

The leak detection report we provide, along with the scope of work to expose and repair the leak, can be given to an insurance company if a claim is being submitted. Following this, Aspect always aim to start repair and reinstatement work the same day.

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