Nobody rings a plumber about water pressure that has been mediocre for a decade. They ring about pressure that changed. A slow decline is not an event, so it never becomes a phone call, and the household simply adjusts: one shower at a time, do not run the washing machine in the morning, that tap has always been like that.
In the estates built from the 1960s around Green Valley, Miller, Cartwright, Ashcroft, Sadleir and Busby, that decline has a specific and entirely predictable cause. Galvanised steel water pipe corrodes from the inside, and the loss is gradual enough that people adapt to it rather than notice it.
Galvanised steel water pipe corrodes internally over decades, and the corrosion products build up on the inside wall so the bore gets progressively narrower. Because it happens over years rather than overnight, the household adjusts instead of complaining. The tell is not a sudden drop, it is discoloured water when a tap is first opened, poor flow that is worse the further from the meter you go, and pressure that gets worse when two things run at once.
- Ask whether it changed suddenly or has always been drifting down
- Look at the water when a tap is first opened after a few hours
- Compare a tap near the meter with one at the far end of the house
- Rule out aerators and part-closed valves first, because they are free
- Get it measured rather than described before anybody quotes work
On this page
1. How galvanised pipe actually fails
Galvanised steel pipe is steel with a protective zinc coating. It was standard for domestic water supply for a long time, and the estates built out here in the 1960s are full of it.
What eventually happens is that the protective layer is exhausted and the steel underneath begins to corrode. Critically, that happens on the inside of the pipe, where nobody can see it, and the corrosion products do not wash away. They build up on the internal wall, so the bore of the pipe gets narrower every year.
A pipe that has lost a substantial part of its internal diameter delivers substantially less water. Nothing has burst, nothing is leaking, and from the outside the pipe looks exactly as it always did.
People describe it as pressure and that is fair enough, but what has changed is how much water can get through. That distinction matters, because a pressure pump will not fix a pipe that has closed up.
2. Why it goes unreported for a decade
A burst pipe is an event and it produces a phone call within the hour. A pipe losing a small percentage of its bore each year produces nothing at all, because human beings are extremely good at adapting to gradual change.
What actually happens is a set of household rules that nobody remembers making. Do not run the washing machine while somebody is in the shower. The back tap has always been weak. Fill the bath before you start cooking. Every one of those is a workaround for a supply that has quietly closed up.
It is worth saying plainly that this is not carelessness. Nobody notices the thing that changed by two per cent a year. But it does mean the question worth asking is not "has the pressure dropped" but "would you accept this pressure if you moved in tomorrow".
3. The tells, in order of usefulness
- Discoloured water on first use. Open a tap that has not been used for several hours and watch the first few seconds. Rusty or brownish water that clears is the most direct evidence there is.
- Worse the further from the meter. More pipe means more restriction. If the outside tap near the meter is strong and the far bathroom is weak, that gradient is the story.
- Much worse when two things run at once. A restricted supply has very little in reserve, so simultaneous demand collapses it.
- Hot worse than cold, or the reverse. Tells you which line is affected, which is useful information rather than a diagnosis.
- Fittings that keep blocking. Aerators and cartridges that clog repeatedly are catching material coming from somewhere upstream.
- No history of a sudden change. This is the confirming one. Gradual is the signature.
4. Check the free things first, honestly
None of the above is a reason to skip the cheap checks, and a good plumber will do them before proposing anything expensive.
- Is the main stop tap at the meter fully open? A tap left part-closed after previous work is genuinely common.
- Are the aerators clear? Unscrew one and look. It is the single most common cause of one weak outlet.
- Is there a filter somewhere with a cartridge nobody has changed?
- Are the isolation valves under the sink fully open?
- Are any flexible hoses kinked or crushed behind a cabinet?
If those are all clear and the pattern above matches, that is a considerably stronger case than either observation alone.
Pressure that has always been poor?
We will measure it at the meter and at the fixture and tell you where it is being lost.
5. What can actually be done about it
A pipe that has closed up internally cannot be opened up again in any lasting way. The material has to be replaced, and the honest question is how much of it.
Sometimes a single restricted section is doing most of the damage, typically the run between the meter and the house, and replacing that alone transforms the result for a fraction of a whole-house cost. That is worth establishing before anything larger is discussed, and measurement is how you establish it.
Sometimes it genuinely is the whole installation. That is a real job and it should be presented as a real job, with a price, rather than crept up on. What it should never be is a first suggestion made without measuring anything.
What will not work is a pressure pump. If the restriction is inside the pipe, pushing harder against it does not create bore that is no longer there, and it puts stress on an installation that has already aged.
6. If you are renovating anyway
The cheapest time to deal with galvanised pipe is when a wall or a floor is already open for another reason, and in a house of this age that opportunity comes along with a bathroom or a kitchen renovation.
Reinstating new tiles and new waterproofing over sixty-year-old supply lines is a decision people make by default rather than deliberately, and it is the one that produces an opened-up two-year-old bathroom later.
The same applies to the run between the meter and the house. If a trench is going in for any reason, that is the moment to ask what else follows that route.
- Galvanised steel water pipe corrodes internally and the bore narrows year on year.
- The loss is gradual, so households adapt to it instead of reporting it.
- The best tell is discoloured water in the first seconds from a tap unused for hours.
- Flow gets worse the further from the meter, and collapses when two things run at once.
- Check the stop tap, aerators, filters and isolation valves first. They are free.
- A pressure pump does not fix a pipe that has closed up. The material has to be replaced.
Pressure that fell slowly FAQs
How do I know if I have galvanised pipe?
Where it is visible, under the house or at the meter, it is grey steel with threaded fittings rather than copper or plastic. The clearest circumstantial evidence is the age of the house combined with rusty water in the first few seconds from an unused tap.
Will a pressure pump fix it?
No. If the restriction is inside the pipe, a pump pushes harder against the same narrow bore, and it stresses an installation that is already old. Anyone proposing one before measuring anything is guessing with your money.
Do I have to replace all of it?
Not always, and it is worth finding out before agreeing to anything. Sometimes one section, often the run from the meter to the house, is doing most of the damage. Measuring at different points is how you tell.
Is rusty water from the tap a health problem?
Anything about water quality and health is a question for your water authority or a health professional rather than for us. What we can say is that it is a strong indicator about the condition of the pipe it came through.
The pressure is fine at the front tap but bad in the back bathroom. Why?
More pipe between the two, so more accumulated restriction. That gradient across a single property is one of the clearest signals that the problem is inside the pipework rather than in the supply.
It got worse suddenly rather than slowly. Same cause?
Probably not. Sudden changes point at something specific: a part-closed valve, a failed fitting, or work somewhere on the system. Gradual is the signature of internal corrosion, and sudden is worth investigating differently.