Water pressure has dropped suddenly
A sudden drop in water pressure across your home can be genuinely worrying, but the good news is that nine times out of ten, it's something straightforward to diagnose. This happens to plenty of UK homeowners—often without warning—and the cause is usually either external (affecting your street) or something simple you can check yourself in minutes. Most commonly, it's a partially closed stopcock, an issue with the water meter isolation valve, or a problem with the mains supply in your area. This guide walks you through the logical checks to identify what's happened, starting with your neighbours and moving inward through your own pipework. If you work through these steps and still can't find the cause, a qualified plumber can rule out less obvious culprits like a failed pressure reducing valve.
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Most likely cause & what to check
A sudden drop in mains water pressure across the whole property most commonly indicates either a street-level supply issue or a partially closed mains stopcock.
Check with your neighbours — if they also have low pressure, contact your water supplier. Check your supplier's website or call their helpline to ask about known works or burst mains in the area.
Check your internal mains stopcock — usually under the kitchen sink or where the mains pipe enters the property. Ensure it is fully open (turn anti-clockwise to open).
If you have a water meter, it is typically located just outside the property boundary in a small chamber. The meter usually has its own isolation valve — check it has not been partially closed.
Check for any visible leaks — a sudden drop in mains pressure can indicate a burst pipe in the internal supply pipework, which would also cause a visible wet patch somewhere.
If the pressure drop cannot be explained by the above, call a plumber — a pressure reducing valve (PRV) that has partially failed can cause a sudden pressure reduction.
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Frequently asked questions
Can low water pressure damage my boiler or heating system?
Most modern boilers have built-in protections and will shut down safely if pressure drops too far, but prolonged low pressure can cause your heating to work inefficiently. It's worth getting the pressure restored quickly—if your boiler has switched off, you'll need adequate mains pressure to restore it.
Should I turn off the stopcock if I find a leak?
Yes, absolutely. If you discover a burst pipe whilst checking for leaks, turning off the stopcock at the mains will stop water flowing to that damaged section and prevent further damage. You can then call your plumber with the problem contained.
How do I know if my stopcock is fully open?
The stopcock handle should be aligned parallel to the pipe when fully open—if it's at right angles to the pipe, it's closed or partially closed. Turn it anti-clockwise until it stops naturally, but don't force it.
Why would the water meter isolation valve get partially closed?
It's usually accidental—someone may have adjusted it during maintenance, or it can slowly creep closed over time if it's not a modern isolating ball valve. Always check it during your diagnostic steps, as it's a quick and easy thing to verify.
If my neighbours have normal pressure, is it definitely my problem?
Almost certainly yes. If they're unaffected, you know the mains supply itself is fine, which narrows the problem down to your internal pipework, stopcock, or meter valve—all things within your property that you (or a plumber) can fix.
How quickly can a pressure reducing valve fail?
A PRV can fail gradually or suddenly depending on the fault. If you've ruled out everything else and pressure loss persists, this is the likely culprit—it's an internal component that a plumber will need to replace or service.