How To Find A Water Leak Under House

Locating a water leak underneath a house without specialist leak detection equipment can cause extensive damage to the property.

If you suspect water leaks underneath your house, it’s best to call a professional leak detection plumber for a full plumbing inspection. Leak detection professionals use specialist equipment to detect water leaks under floors and foundations, or within cavity walls. The specialist equipment includes thermal imaging cameras, acoustic leak detection devices, tracer gases and moisture meters.

There are 6 types of water-carrying pipes buried under the floor of a house which can leak; water mains, hot feed pipes, cold feed pipes, central heating pipes, drainage pipes and underfloor heating piping.

Undetected leaks can cause severe water damage to your home – and water damage restoration doesn’t come cheap!

Signs of a water leak include a high water bill, damp or mould in a room or a boiler losing pressure.

Homeowners can look for signs of a leak or use the water meter to confirm if the property has a water leak. If you notice irregular readings on your pressure gauge or flow meter when the shutoff valve is closed, you have a leaking pipe on your property.

It is the property owner’s responsibility to find, fix and repair the damage caused by a water leak, including pipe and foundation repair.

water leaking under house

Types of Water Leaks Under a House

There are 7 types of leaks that can occur under your home:

1. Mains water pipes

  • Pipe type: Mains pipes supply water to your house directly from the main water line.
  • Water leak causes:
  • Increased system pressure
  • Corrosion of essential plumbing system components (including pipes, valves, and fittings)
  • Damaged seals and valves
  • Debris blockages


Leak detection professionals need to assist with mains water leaks as a pipe replacement, or joint/fixture repair is often needed.

2. Central heating pipes

  • Pipe type: Central heating pipes are traditionally made from copper, but steel or plastic PVC components are also used. These pipes circulate heating and hot water from boilers to radiators to spread warmth throughout homes. They also supply appliances such as washing machines, water heaters, and dishwashers with hot water.
  • Water leak causes:
  • Excessive boiler pressure
  • Corrosion
  • Faulty pressure release valves
  • Older systems
  • Poor water quality
  • Loose fittings and connections


Apart from a visual inspection, heating leak detection experts will use thermal imaging cameras, moisture meters, acoustic devices, and dye and pressure tests to locate hidden leaks within plumbing systems and appliances.

3. Cold feed pipework

  • Pipe type: A cold feed water pipe transports cold water to and from the boiler unit. These pipes are also connected to irrigation systems.
  • Water leak causes:
  • Excess condensation – leading to frozen pipes
  • Corrosion
  • Wear and tear (i.e. age of boiler system or pipework)
  • Loose fittings, connections, or valves
  • Increased water pressure

If you suspect a cold water pipe leak it’s best to contact leak detection experts for your leak repair. A mains water supply or irrigation leak can cause water to seep under foundations, driveways or gardens.

4. Hot feed pipework

  • Pipe type: Hot water pipes carry hot water from the boiler unit to radiators, appliances, and underfloor heating.
  • Water leak causes:
  • Increased system pressure
  • Too high temperatures
  • Excessive thermal expansion and contraction
  • Corrosion
  • Faulty thermostat/temperature sensor
  • Wear and tear
  • Poor installation
  • Damaged connections, seals, valves, or joints
  • Cracked heat exchanger


Signs of these pipe leaks include water stains on floors and walls, dripping radiators and boilers, or unusual plumbing sounds throughout your house.

5. Underfloor heating piping

  • Pipe type: PEX (cross-linked polyethylene) is the most common material used for underfloor pipes due to its flexibility and heat resistance. Underfloor heating pipes circulate hot water underneath floors.
  • Water leak causes:
  • Installation issues
  • External factors (e.g. drilling, shifting floor boards, hydrostatic pressure)
  • Wear and tear
  • High system pressure
  • Corrosion – in older systems with metal pipes
  • Oxygen diffusion
  • Damaged pipes, valves, seals, or connections
  • Lack of regular maintenance


Prevention tip: Annual maintenance of underfloor heating systems is recommended to keep plumbing systems in top condition – including pipe, fixture, drainage, and appliance maintenance.

6. Drainage pipes

  • Pipe type: Drainage pipes are made from materials such as PVC plastic, cast iron, or cement. These pipes carry wastewater from your plumbing system to the main sewer line.
  • Water leak causes:
  • Wear and tear (e.g. age of pipes)
  • Corrosion
  • Increased water pressure
  • Worn-out seals, valves, joints, or connections
  • Temperature fluctuations
  • Ground movement (e.g. root intrusion, shifting soil, moving exterior walls)
  • Blockages


Regularly conduct visual inspections of drainage pipes on your property. Remove any blockages, like soil or leaves, to keep pipelines clear.

7. Concrete slab leaks

  • Type: Hidden water leaks in underground pipes cause plumbing leaks through concrete slabs. This type of plumbing leak is more common in older homes where copper pipes are used. Underground irrigation leaks running beneath driveways can cause slabs and fountains to crack.
  • Water leak causes:
  • Corrosion
  • External factors such as shifting soil or root intrusion
  • Poor installation
  • Frozen pipes
  • Increased water pressure


Leak detectors are needed to locate and repair water leaks and burst pipes under concrete slabs.

Signs of a Leak Under a House

The symptoms of a leak under a building include:

  • Cold or lukewarm radiators
  • Intermittent heating or fluctuating temperatures
  • Increased water meter readings and water bills
  • Reduced system pressure or less water supply
  • Musty smells
  • Mould and mildew growth
  • Excessive moisture (i.e. condensation)
  • Water stains on floors
  • Unexplained puddles of water
  • The sound of running water – hissing, gurgling, or bubbling
  • Change of material texture such as warped floorboards or bubbled paint

Who is Responsible For Water Leaking Under a House?

The responsibility for a water leak inside the property boundary falls with the property owner.

Property owners must maintain mains water lines on their side of the water meter and are responsible for the cost of lost water and water leak repair. This applies to the repair and maintenance of the mains shut-off valve too.

Water suppliers are responsible for the maintenance and repair of water leaks on their side of the water meter, including shut-off valves.

Use The Water Meter Test To Check For Leaks

The water meter leak test can be used to confirm if a house has a water leak. It’s an effective and simple test for homeowners to perform. The only type of leak the water meter test will not detect is a combi boiler central heating system leak.

Find the water meter outside your house near the property line, often in a covered box or underground pit, then follow this step-by-step guide:

  1. Take an initial reading – one full dial rotation is equivalent to 1 litre of water.
  2. If the meter continues to spin when no water is being used, there is a water leak on your property.
  3. Repeat the test with the internal stopcock shut off. This will identify where the water leak is.
  • Water leaks before the internal stop tap = a leak on the incoming water supply line
  • Water leaks after the internal stop cap = a leak on your property


Note: Not all leaks are visible.

Hidden leaks can be found underneath floors, central heating, leaking toilets or from swimming pools.

Choose ADI Leak Detection To Trace The Leak Under Your House

To find hidden leaks on your property, contact ADI Leak Detection. Our team of plumbing and heating experts are equipped to find water leaks with the least amount of disruption.

Our non-destructive leak detection equipment includes tracer gas, acoustic listening devices, borescopes, and thermal imaging cameras.

Call our friendly team on 0800 731 3843 for assistance with any water leak under your house!

Adrian Morgan

Adrian Morgan CIPHE RP RHP is the founder & Managing Director of ADI Pro Leak Ltd. Adrian is also the Head Plumbing, Heating & Leak Detection engineer at ADI Leak Detection.

Adrian CIPHE RP RHP is proud to be registered with the Chartered Institute of Plumbing & Heating Engineering, a Registered Plumber and a Registered Heating Professional.