Low water pressure at every tap usually means a part-closed stopcock, a mains supply issue, or a leak reducing flow before it reaches the house. Low pressure at just one outlet is more often local: a clogged aerator or a stiff isolation valve. Check the stopcock first. If pressure stays low across the whole property, especially with a rising bill, a hidden leak on the supply pipe is worth ruling out.
Weak flow from every tap, a shower that's lost its punch, or a toilet that fills slowly can have several different causes, and not all of them are plumbing faults you can fix in five minutes. This guide walks through how to tell whole-house pressure loss from a single-outlet problem, what usually causes each, and when low pressure is actually a symptom of a leak rather than a nuisance on its own.
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Whole house or one outlet? Start here
The single most useful diagnostic question is whether the problem affects every tap in the property or just one. It changes where you should look entirely.
- Whole house: points to something upstream of the whole system, the stopcock, the incoming supply pipe, or the mains itself.
- Single outlet: points to something local to that fixture, a blocked aerator, a kinked flexible hose, or a part-closed isolation valve under the sink.
If it's genuinely whole-house, work through the checks below in order, since the simplest and most common cause is also the easiest to check.
Check the stopcock first
The internal stopcock, usually located under the kitchen sink or occasionally in a utility room or cellar, controls the flow of water into the entire house. If it's only partly open, either because it was never fully opened after work on the system or has slowly closed over years of vibration, every tap in the house will feel weaker than it should.
- Locate the stopcock and check which way it's turned.
- Turn it anticlockwise as far as it will comfortably go, without forcing a stiff or old valve.
- Run a tap for a minute and see whether flow improves noticeably.
If the stopcock was already fully open and pressure is still weak, move on to the other causes below rather than assuming it's fixed.
Other common causes of low pressure
Local, single-outlet causes
- A clogged aerator or showerhead filling with limescale, especially in hard water areas.
- A kinked or degraded flexible supply hose behind a washing machine, dishwasher or under a basin.
- A partially closed isolation valve fitted under an individual sink or toilet.
Whole-house causes
- A fault or planned works on the water supplier's mains network, which is usually temporary.
- A narrow or old lead or galvanised supply pipe that restricts flow more than modern plastic pipe.
- Higher demand at peak times, such as early morning, in areas with an already limited supply.
- A leak on the supply pipe between the boundary and the house, which diverts water and pressure before it reaches your taps.
What's normal for UK mains pressure
It helps to know roughly what to expect before deciding something is wrong.
| System | Typical pressure | Notes |
|---|---|---|
| UK mains water supply | Roughly 1 to 4 bar | Varies significantly by area, elevation and time of day. |
| Boiler or central heating (cold) | Typically 1 to 1.5 bar | A separate sealed system; this is not the same measurement as mains water pressure. |
Rural and elevated properties commonly sit toward the lower end of the mains range as a matter of course, which is a separate question from whether something has actively gone wrong.
When low pressure points to a leak
South West Water is responsible for the mains up to the boundary of your property, and homeowners are responsible for the private supply pipe running from that boundary or stop tap into the house. A leak anywhere along that private run reduces the pressure and volume reaching your taps, since water is escaping into the ground before it gets to you.
This is more likely to be the explanation when the drop is gradual rather than sudden, affects the whole house rather than one tap, and comes alongside other signs: a water bill that's crept up with no change in usage, a damp or unusually green patch of ground outside, or a meter that keeps turning when every tap in the house is off. South West Water runs a leak allowance scheme for metered customers in some circumstances, with conditions attached including evidence of repair, which is worth checking once a leak is confirmed.
Non-invasive water leak detection using acoustic sensors, tracer gas and thermal imaging can confirm whether a leak on the supply pipe explains a pressure drop, without digging up the garden or driveway to find out. Where the issue sits specifically on the mains-side run, our mains water leak detection service is built for exactly this.
Rural Cornwall and Devon pressure
Away from town centres, Cornwall and Devon properties are often fed by longer rural supply pipes, sometimes running for hundreds of metres from the nearest main, and elevation plays a real part too: a farmhouse or cottage sitting well above the local network reservoir will naturally see lower pressure than a bungalow down in the valley. That background reality makes it harder to judge by feel alone whether pressure has genuinely dropped or has simply always been on the lower side. We see this most often on older rural connections and smallholdings, where a long-standing modest pressure suddenly gets worse, which is usually the more telling sign than the absolute level.
Frequently asked questions
Why has my water pressure suddenly dropped?
A sudden drop across the whole house often means a part-closed stopcock, a fault on the supplier's mains, or a new leak somewhere on the pipe run. If it happened after work on the property, such as a stopcock being touched or a repair nearby, check that first. A gradual, worsening drop is more often a leak or a narrowing pipe.
Is low water pressure a sign of a leak?
It can be. A leak on the supply pipe between the mains and the house diverts water and pressure before it reaches your taps, so pressure drops as a side effect. It's more likely to be a leak if the drop is gradual, affects the whole house, and comes with a rising water bill or a damp patch outside.
Why is only one tap in my house affected by low pressure?
A single affected outlet usually points to something local: a clogged aerator or showerhead, a partially closed isolation valve under that fixture, or a kink in flexible supply hose. Whole-house causes such as a leak or a mains restriction affect every tap in the property.
How do I check if my stopcock is fully open?
Find the internal stopcock, usually under the kitchen sink, and turn it anticlockwise as far as it will comfortably go without forcing it. If it was only part-open, you should notice an improvement in flow within a minute or so of running a tap. Never force a stiff, old stopcock; call a plumber if it won't move.
What water pressure is normal for a UK house?
Mains water pressure in the UK typically runs at around 1 to 4 bar, though this varies by area, and rural or elevated properties often sit toward the lower end. Boiler and heating system pressure is a separate measurement, typically around 1 to 1.5 bar when cold, and shouldn't be confused with mains water pressure.
Why is water pressure often lower in rural Cornwall and Devon properties?
Rural supply pipes are often longer, older, and can include narrower sections or more bends than a modern estate connection, all of which reduce pressure naturally. Elevation matters too, since a property higher than the local network reservoir will see lower pressure than one lower down, independent of any fault.
When should I get low water pressure professionally investigated?
If you've ruled out a part-closed stopcock and a blocked aerator, and pressure is still low across the whole house, especially alongside a rising bill or unexplained damp, it's worth getting the supply pipe checked. Non-invasive leak detection can confirm whether a hidden leak is behind the drop before anything is dug up.
Pressure still low after checking the basics? Let's find out why
If you've ruled out the stopcock and an obvious blockage and pressure is still weak across the house, we'll check the supply pipe for a hidden leak across Cornwall and Devon.
Call Dickie on 07822 025 911 No Find, No Fee on residential leak detection (subject to terms)