A shower that has lost its force or a kitchen tap that takes twice as long to fill a kettle is annoying, and most people assume the water company is to blame. Sometimes it is. But low pressure can also be the first sign of water escaping from the pipe between the boundary and your house, long before a wet patch or a high bill appears. The trick is to rule out the simpler causes in a sensible order.
This guide covers when low pressure points to a leak on your supply pipe, what else it could be, the checks you can do yourself, and how a survey confirms it.
Can a water leak cause low water pressure?
Yes. Pressure and flow are linked. Water that escapes from a split or a failed joint on your supply pipe is water that never reaches your taps, and the more water is lost, the less flow is left for the house. A small leak may make no noticeable difference. A larger one, or a small one that has grown, can leave upstairs taps weak and make the shower falter whenever another tap is opened.
A supply pipe leak tends to produce a pattern: the drop is felt across every mains-fed tap, it does not recover at quiet times of day the way a network problem often does, and it may get worse over weeks rather than coming and going.
What else causes a sudden drop in water pressure?
| Cause | Typical signs | Quick check |
|---|---|---|
| Burst main or work on the network | Sudden drop, neighbours affected, sometimes cloudy or discoloured water | Ask neighbours and check your water company's service updates |
| Peak demand | Weaker in the morning and early evening, normal at other times | Compare the flow at different times of day |
| Stopcock or outside stop tap partly closed | Drop started after plumbing work, a meter fitting or a visit from the water company | Check the internal stopcock is fully open |
| Shared supply | Pressure falls when a neighbour uses water | Note whether the drop matches neighbours' use |
| Problem at one outlet | Only one tap or shower is weak | Clean the aerator or shower head and check its isolation valve |
| Hot water side only | Cold taps are fine, hot is weak | Points to the boiler, cylinder or their valves rather than the supply |
| Leak on the supply pipe | Every mains-fed tap weaker, no recovery at quiet times, meter moving with nothing on | Meter test with the internal stopcock closed |
Is the low pressure only in your home?
Start outside the house. Ask neighbours whether they have noticed a change, and check your water company's website or service line for work or bursts in your area. If the whole street is affected, the cause is almost certainly on the network and there is little point looking for a leak on your own pipe.
Water companies in England and Wales work to a minimum pressure standard. The Consumer Council for Water explains that companies should maintain a minimum of seven metres static head, which is 0.7 bar, in the communication pipe that runs from the main to your outside stop valve. The same guidance makes clear that the company has no obligation for pressure inside your private supply pipe, whether it is shared or not, or inside your home. That is the part a leak survey looks at.
If you believe the pressure reaching your boundary is low, the Consumer Council suggests keeping a record of when it happens and reporting it to your water company, which can test the pressure.
Is your stopcock fully open?
A stopcock turned partly closed restricts the flow to the whole house and is one of the most common reasons for a sudden change. It often happens after a plumber has worked on the system or after the valve has been used in an emergency.
Turn the internal stopcock anticlockwise until it stops, gently, then back a small amount so it is not jammed. Old brass valves can start to weep at the spindle when turned after years untouched, so keep a cloth handy. If the outside stop tap was recently operated by someone else, such as for a meter fitting, it is worth asking the water company whether it was fully reopened.
Which taps are affected?
Knowing how your water is fed avoids chasing the wrong problem.
- The kitchen cold tap is almost always fed directly from the mains, so it is the best indicator of supply pressure.
- Taps fed from a loft tank run at low pressure by design, because the pressure comes only from the height of the tank. A weak flow from these is not in itself a sign of a supply leak.
- A combi boiler or unvented cylinder takes mains pressure, so a supply problem affects the hot water too.
- One weak outlet usually has a local cause, such as a blocked aerator, a scaled shower head or a half-closed isolation valve.
How can you check for a supply pipe leak yourself?
If you have a water meter at the boundary, a meter test is the key check.
- Turn off every tap and appliance, and wait for toilet cisterns and any storage tank to finish filling.
- Close the internal stopcock fully and open the kitchen cold tap to confirm the water stops.
- Read the meter, or watch its flow indicator, then wait at least half an hour without using water and read it again.
- If the meter has moved with the stopcock closed and holding, water is escaping between the meter and the stopcock.
A simple flow test also helps, especially without a meter. Time how long the kitchen cold tap, fully open, takes to fill a bucket of known size, and work out the litres per minute. Repeat it at the same time of day over a week or two. A figure that keeps falling, when neighbours report no change, is worth noting and passing to the engineer. Our guide to unexplained high water usage covers the other checks inside the house.
What does a gradual drop over months suggest?
Not every pressure problem is sudden. A slow decline can come from a leak that is growing as water washes away the ground around it. It can also come from the pipe itself: old iron pipe can build up corrosion inside, and older supply pipes may simply be too narrow for a modern household. A leak survey helps separate these, because a pipe that is narrowed but sound will pass a meter test, while a leaking one will not.
How does a survey confirm a leak on the supply pipe?
The engineer works from measurements first, then location.
- Readings at the stopcock. Pressure and flow are measured where the supply enters the house and recorded for the report.
- A controlled meter test, after confirming the stopcock holds.
- Listening at the fittings. A leak on a metal pipe can often be heard at the stopcock or outside stop tap with the house quiet.
- Tracing the route from the boundary to the house, since old pipes rarely run in a straight line.
- Pinpointing the leak with a ground microphone, a correlator or tracer gas, depending on the pipe material and the surface above it.
- Marking and reporting the position, so a repair needs only one small excavation.
Our article on underground supply pipe leak detection explains how each of those tools works and where each struggles.
When should you call a leak detection specialist?
Call when neighbours are unaffected, the stopcock is fully open, the drop affects all your mains-fed taps, and especially when the meter moves with the stopcock closed. It is also worth calling if the flow keeps falling week after week or a wet patch has appeared outside.
Our water mains leak detection for underground and supply pipe leaks is £300 to £500. Call 020 3912 0200 with your meter and flow readings to hand.
Frequently asked questions
Why has my water pressure suddenly dropped?
The most common reasons are work or a burst on the water company's network, a stopcock left partly closed, or a leak on your supply pipe. Asking neighbours and checking your stopcock rules out the first two quickly.
Can a leak outside the house reduce water pressure inside?
Yes. Water escaping from the supply pipe before it reaches the house reduces the flow available at your taps, and a larger leak can noticeably weaken every mains-fed outlet.
What is the minimum water pressure a water company must supply?
The Consumer Council for Water says companies should maintain at least seven metres static head, or 0.7 bar, in the communication pipe up to your outside stop valve. The standard does not cover your own supply pipe or plumbing.
Why is only my hot water pressure low?
If the cold taps are fine, the supply pipe is unlikely to be the cause. Look at the boiler, the cylinder and the valves on the hot water side, and ask a heating engineer to check them.
How do I test for a supply pipe leak without a meter?
A timed bucket test repeated over several days shows whether flow is falling. A specialist can then listen at the stopcock and trace the pipe to confirm a leak.
