Grange PlumbingWhy has my water pressure suddenly dropped?
A sudden drop in water pressure usually means one of five things: an internal plumbing fault (a partly closed stop tap, blocked filter or failed PRV), a leak on your underground supply pipe, an old lead or galvanised pipe finally restricting flow, a stop tap that's seized or partly shut, or a temporary issue with your water company's main. Working through these in order usually identifies the cause within minutes.
Is it just one tap or the whole house?
Start with this question — it narrows the cause immediately. If only one tap is affected, the problem is internal and local: a blocked aerator, a clogged isolating valve under the sink, or a failed tap cartridge. If every tap in the house has dropped at the same time, the problem is at or before the point where the water enters the house — the stop tap, the supply pipe, or the water company's side.
Internal plumbing issues
If the whole house is affected, internal causes are still possible.
Partly closed internal stop tap
The most common — and easiest to fix. Internal stop taps occasionally get knocked or left partly closed. Open it fully (anticlockwise) and see if pressure restores.
Pressure reducing valve (PRV) failure
Newer homes often have a PRV at the incoming main. They can fail closed, choking the whole house. Replacement is a quick plumber job.
Blocked incoming filter
Some installations include an inline filter on the incoming supply. If it hasn't been changed for years, it can clog and starve the house of flow.
Scale build-up in old pipework
In hard-water areas, decades of scale inside old copper or galvanised pipework can reduce internal bore enough to drop pressure noticeably.
External supply pipe leaks
A leak on the underground supply pipe between the boundary and the house is one of the most common causes of a sudden drop in pressure — and one of the most expensive if ignored. Water escapes underground and pressure at the house falls. Look for damp or boggy patches over the pipe route, an unusually green lush strip of lawn in dry weather, or paving that has started to tilt. The fastest test: turn everything off and check whether the external water meter is still ticking. Our leak detection service can pinpoint the exact spot non-destructively.
Old lead or galvanised supply pipes
Lead, galvanised steel and pinholed old copper supply pipes all restrict flow as they age. Galvanised steel rusts from the inside, narrowing the bore. Lead pipes soften, dent and partly crush over decades. If your pressure has fallen gradually over years rather than overnight, and your pipe is older than 40 years, the pipe itself is the bottleneck. Replacing it with 25mm MDPE typically restores full pressure immediately. See 7 signs your supply pipe needs replacing.
Stop tap problems
Two stop taps matter: the internal one inside the house and the external one at the boundary. Both can seize or partly fail — often noticed only when someone tries to turn the water off. A partly seized external stop tap can choke flow even when it looks open. If you can identify the boundary stopcock (usually a small metal cover marked 'W' on the pavement or just inside your boundary), your water company will normally inspect and replace it free of charge.
Water company issues
Before doing anything else, ask your neighbours. If their pressure has also dropped, the cause is on the water company's side — a burst main, planned works or a temporary supply switch. Your water company's website will usually show live incidents by postcode. These typically clear within hours. If only your house is affected, the issue is on your side and worth investigating further.
When leak detection is the right next step
If you've ruled out internal causes and your meter is ticking with everything off, the next step is a professional leak detection survey. We use acoustic detection, thermal imaging and tracer gas to pinpoint the exact position of a buried leak without digging speculatively. This gives a proper diagnosis and lets us quote accurately for either a targeted repair or a full replacement. See our leak detection service.
When to replace the water main
Replacement (rather than repair) is the right call when: the pipe is lead, galvanised or pre-1990s copper; you've had repeat leaks; pressure has dropped gradually over years; or the cost of repeated repairs is approaching the cost of a fresh MDPE installation. Modern moling means the new pipe can be installed in a single day without disturbing the driveway or garden. See our water main replacement service and moling service for how it works.
Quick diagnostic checklist
Run through this in order before calling anyone out: 1) Is it just one tap or every tap? 2) Are your neighbours affected? 3) Is your internal stop tap fully open? 4) With everything off, is the external water meter still ticking? 5) Are there damp patches over the pipe route? Answers to these five questions almost always point to the cause within minutes.
How we can help
We carry out leak detection, supply pipe replacement and moling installations across Sussex and Surrey every week. Free site visit, fixed price, no call-out fees. Call or WhatsApp 07894 956041.
Frequently Asked Questions
Why has my water pressure suddenly dropped?
The most common causes are a partly closed stop tap, a leak on your underground supply pipe, an aged lead or galvanised pipe, a failed pressure reducing valve, or a temporary issue with the water company's main.
How can I tell if my supply pipe is leaking?
Turn off every tap and appliance and check your external water meter. If it is still ticking, water is flowing somewhere — usually on the buried supply pipe between the boundary and the house.
Will replacing a lead pipe improve water pressure?
Yes, almost always. Old lead and galvanised pipes restrict flow as they age. Replacing with 25mm MDPE typically restores full pressure immediately.
Who do I call about low water pressure — my water company or a plumber?
Ask your neighbours first. If they are affected too, call your water company. If only your house is affected, call a plumber to check the internal plumbing and supply pipe.
Can a partly closed stop tap really drop my pressure?
Yes — it's one of the most common causes of a sudden pressure drop and one of the easiest fixes. Always check the internal stop tap is fully open before doing anything else.
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