Old galvanised pipes and the slow drop in water pressure

Why does the water run fine at the gate but trickle from the kitchen tap? In older homes, old galvanised pipes rust shut from the inside and choke your pressure.

Interview by Tomek Korzeniewski · with Zaid Petersen, Owner and master plumber

What was used back then?

Older pipes hide their own kind of trouble. Galvanised steel was the pipe of choice in homes built between the fifties and the seventies. Petersen says it is steel pipe coated in zinc to stop it rusting. That was the normal choice at the time and it did a good job for a few decades.

The trouble starts inside the pipe. Petersen explains that the zinc wears away from the inside first. Once it's gone, the bare steel starts to rust.

Rust in a water pipe does more than make holes. He says it builds up on the inside wall like scale in a kettle, only worse. Over sixty years, a pipe that started at twenty millimetres inside can close down to a gap the size of a pencil.

So that's where the low pressure comes from?

So a pencil-wide gap does not always show at the meter. Very often it hides there. The reading is fine.

Here's what that tells him. He walks into the kitchen and the tap is a trickle, even though the water is fine at the gate. It is getting strangled on the way through the old pipes.

The gap between the meter and the kitchen points straight back inside the property.

What other signs should people look for?

Those walls hide more clues once you know what to watch for. Petersen says to look for brown or orange water when you first open a tap in the morning, especially after a holiday. That colour is rust coming loose.

The next clues are about how the water moves. Pressure that's fine at one tap and weak at another. A shower that swings cold or scalding when someone flushes a toilet. Small leaks keep appearing in different spots, often where a pipe runs into a wall or through a floor. The pattern itself is a sign.

One more thing to check for yourself. Petersen says that if you can see a pipe, look at the threaded joints. Galvanised pipe is joined with threads and that is where it fails first. The threading makes the wall thinner, so that's the weak point.

What else causes low pressure?

A thin wall is not the only thing that drops your pressure. Plenty of cheaper faults cause the same symptoms.

The usual suspects are quick to fix. A pressure control valve that has failed or been set too low. A stopcock left only half open, which happens more than you'd think after a repair. A blocked filter on the inlet. A shower head full of scale. A mixer tap with a clogged aerator.

We check all of those before anything else. Petersen says they are cheap and quick to sort out. Clear the easy faults and the pressure often comes right on its own. If it stays bad after that, only then does he look at the pipes themselves.

How do you check the pipes without breaking walls?

The readings do most of the work. Petersen takes pressure and flow readings at different points in the house. If the flow drops a lot between the meter and the first tap, the main line in the ground is the culprit.

If it's fine at the first tap and bad at the far bathroom, the trouble is in the branch running through the roof or the walls.

Seeing the inside is usually the deciding moment. Petersen says that when you look inside a sixty-year-old galvanised pipe, the decision makes itself. Customers want to see it too, so he keeps the piece for them to hold.

When do you recommend a full repipe?

One sign on its own is easy to live with. Several at once tells a different story.

Patching one leak on a pipe like that gets you nowhere. He compares it to fixing one rusty spot on an old car. The next one is already on its way.

The line comes down to how much of the house is affected. If the galvanised pipe is throughout and showing all the signs, Petersen says a repipe is the honest answer. If only one section is bad, say the main line from the meter, he can replace just that and leave the rest for later.

What do you replace it with?

So which pipe does he reach for? Copper or a modern plastic system, depending on the house. Petersen says copper is tough. It handles the heat near the geyser well. Plastic runs quicker through roof spaces and doesn't corrode, which matters down here with the salt in the air.

Often it is a mix of the two. Copper around the geyser, plastic for the long runs. Whatever he uses, Petersen says it's installed to the national plumbing standards. He signs it off himself.

Swapping out the old galvanised pipes and low pressure for new copper or PEX is the heart of a pipe replacement (repiping) job. The old pipe comes out. The new pipe goes in, with as little cutting as the route allows. For wider background, see Plumbing Information for Home Owners (Saint Paul Minnesota).

How disruptive is a repipe?

Less than most people fear. Petersen says that in most of these houses the pipes run through the roof and drop down inside the walls to each tap.

The work follows that same route. New pipes go through the roof, then a narrow channel gets chased in the wall to each point. Floors and furniture get covered, the cuts are neat and the channels get plastered closed afterwards. You will need a painter for those patches.

For an average three-bedroom house it runs a few days. Petersen says they keep the water on every evening so the family can cook and shower. Nobody is left without water overnight.

What about the underground line from the meter?

The old main line is often the worst section of the lot.

Replacing it means digging. He digs a trench from the meter to the house, lays the new pipe and backfills it. If a paved driveway is in the way, he tries to go around it or tunnel under.

There's a bonus in doing this line. Petersen fits a proper stopcock where the pipe enters the house, which a lot of these old properties never had. That one thing makes future repairs much easier.

Does fixing the pipes affect the geyser?

Can an old geyser really cave in from a repipe? It can. Petersen explains that once the pressure comes back up, an old geyser that has sat on weak pressure for years suddenly gets full pressure again.

That sudden change can be the tipping point. If there's no pressure control valve, or the geyser is old and tired, he says that can be the moment it gives in.

So he plans for it. Better to plan that in than get a call two weeks later.

Ready when you are

If you would like to take this further, Pipe replacement (repiping) is the place to start.

About the expert

Zaid Petersen, Owner and master plumber, Klipspringer Plumbing.

Frequently asked questions

Can galvanised pipes be cleaned out instead of replaced?

Not really, once the rust has built up inside. Scrubbing or flushing might shift loose debris near the surface, but the rust that's narrowed the pipe is bonded to the metal, not sitting loose in the water. Clean it today and the same pipe keeps rusting from the inside tomorrow, because the zinc coating that was protecting it is already gone.

How can I get better pressure without replacing anything?

If the pipes themselves aren't the problem, there are a few things worth checking first. A stopcock that's only half open, a scaled-up shower head, a clogged aerator on a mixer tap or a blocked inlet filter can all steal pressure and cost nothing to fix. If those check out fine and the pressure is still weak, the restriction is most likely inside the old pipework and no amount of adjusting will get past that.

Do I need a plumber for water hammer, or is it something else?

Water hammer, that bang in the pipes when a tap shuts, is usually about trapped air or loose pipe fittings rather than old galvanised pipework. It's a different fault to weak, steady low pressure. Worth mentioning when you call someone out, because the fix is not the same as the fix for narrowed pipes.

Can I check myself whether my pipes are galvanised before I call anyone?

Yes, if you can see any exposed pipe, in the roof, under a sink or where it comes through a wall. Galvanised pipe is dull grey steel joined with screw threads, not the copper-orange colour or the plastic look of newer pipework. A magnet will stick to galvanised steel but not to copper, which is a quick way to tell them apart if you're not sure by eye.

Will I be overcharged for something simple like fixing a valve or a tap?

A simple fault like a worn valve or a scaled-up tap should cost a fraction of a repipe, because it's a part swap, not a job that involves opening walls or roofs. If a quote for something small feels out of proportion to the work, ask what exactly is being replaced and why, before you agree to anything.

What should I ask a plumber before agreeing to any repipe work?

ask what led to the diagnosis and get a clear explanation of what they found. Ask whether the whole house is affected or just one section, since that changes how much work is actually needed. And ask what the quote covers in writing, so there's nothing added once the walls are open.

About the author

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