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The following information has been sourced from the Ringley Group Factsheet ‘Cracked Water Mains Pipe’.

The pressure of the water that reaches property reduces depending on the number of stories above ground the incoming water mains has to rise. Water pressure will also be reduced by each spur off the mains entry pipe into a property. Typically an incoming water mains pipe will be 25mm blue plastic pipe although some older blocks of flats may still have lead or iron pipework. Ideally this should be replaced as lead pipework can cause health and safety risks and iron pipework is prone to rusting.

Points Of Entry

The typical points of entry for a water main are underneath a floor slab. Water mains pipes may directly feed appliances or feed directly into a water storage tanks/cistern    installed at attic or roof level. Where water storage tanks/cisterns are installed at high level then appliances are gravity fed from the stored water as opposed to mains fed from the incoming water mains. This may be advantageous in areas where water pressure is particularly low or where a dwelling is at high level as water pressure will significantly reduce at around the third or fourth floor level of a building.


A leak from a water mains pipe arises from a defective in-let pipe, usually before it reaches an appliance. This is because most appliances, i.e. baths, hand basins, kitchen sinks, boilers, toilet cisterns, cold water storage tanks, and immersion tanks are fitted with fail safe devices known as overflows which direct a water leak outside the building.

Leaks after the first stop cock into the building (but before the water mains reaches any particular flat) are the responsibility of the freeholder/management company. Generally leaks before the first stop cock into the building are the water supplier’s responsibility. Water leaks, leases & insurance claims policies usually cover the cost of tracing a leak and damage caused by the leak, but it is unusual for the replacement a defective pipe to be covered.

Diagnostic Questions

Mains pressure water leaks are arguably the most serious type of water leak that can occur as they can only worsen due to water pressure maximising any weak joint or other defect in the pipework.

  1. When did the leak occur? – mains water leaks usually start suddenly, not over a period of time;
  2. Is the leak getting worse? – mains water leaks will only get worse;
  3. How fast is the leak occurring? – mains water leaks will fill a bucket fast;
  4. Is the water clean? – mains water leaks can only be clean water;
  5. How long has the leak been going on for? – mains water leaks will not stop, unlike a leaking washing machine that will stop once water in the drum has emptied, or a leaking shower/bath that will stop once the shower has stopped being used, or a leaking central heating system that will stop once the central heating system has drained;
  6. Are all appliances turned off and if so can running water be heard near the inlet?  – mains water leaks will draw water even if every appliance is turned off/shut down;
  7. Has the water been turned off at the stopcock? –  these are usually located in a riser cupboard just outside the flat, under the kitchen sink, in a service cupboard on the ground floor of the common parts, or in a service hatch outside the communal entrance (external mains may either be hand operated taps or need a special water board tap key to turn on and off).

If a mains water leak cannot be resolved then the Fire Brigade should be called. In
such instances they will be able to isolate the water supply, but they are also likely to shut down the electrics to affected areas for obvious safety reasons. If they believe the problem is the responsibility of the water authority they will have access to emergency contact numbers to assist.


  1. Use a specialist plumber because a diligent approach to appointing plumbers is essential, such as checking references etc;
  2. Appropriately specifying appliances such as cisterns, power showers etc. The installation/replacement can be expensive meaning the cheapest with a short life is often a false economy;
  3. Understanding the potential issues and remaining vigilant for symptoms such as cracking, watermarks or damp patches is essential.


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