Water hammer in Singapore homes: the bang
Your pipes bang when you turn off a tap because the water inside was moving and suddenly has nowhere to go. Water barely compresses, so when a valve closes in a split second, the moving water sends a pressure surge back along the pipe. The pipe jolts against its clips or the wall, and you hear a thud. That pipe banging when tap off is water hammer in its plainest form.
In Singapore flats, two fixtures set it off more than any others. A single-lever mixer tap can be flicked shut far faster than an old screw-down tap. A washing machine is the other usual culprit: its inlet valve opens and snaps shut on its own during a cycle, so the knock can come from the service yard while nobody is near a tap.
A slow gurgle at the floor trap while the washer drains is not hammer. That is a drainage problem, covered in the guide on a washing machine drain choke.
Noisy water pipes: match the sound
You can deal with noisy water pipes much more easily once you can name the sound. Ask someone to open and close the tap while you stand by the wall or cabinet, and note the exact moment the noise starts.
| Sound | When you hear it | Likely cause | Who to call |
|---|---|---|---|
| Bang or thud | As a tap or appliance valve shuts | Water hammer, often with high pressure or loose clips | Licensed plumber |
| Steady hum | While water is running | High pressure or a partly closed valve | Licensed plumber |
| Ticking or creaking | As hot water runs and as pipes cool | Hot pipes expanding against clips or brackets | Licensed plumber if loud or new |
| Whistle | At the tap while it runs | Worn washer or cartridge, or a partly closed valve | Licensed plumber |
| Gurgle | At a drain or floor trap | Slow drain or partial choke | Plumber for choke clearing |
If the hum comes with weak flow at some taps, the article on low water pressure at home covers the opposite problem. In a condo, report a hum you can hear from a common corridor or riser to the management office first.
Pressure and the 35 metre rule
PUB's water fittings maintenance infographic asks households to keep the water pressure in all pipes under 35 metres head, and warns that excessive pressure leads to higher flow and waste. Metres head expresses pressure as the height of a column of water, and you cannot judge it by eye.
The clues you can spot are practical ones: taps that gush when barely opened, water splashing out of the basin, and bangs after most shut-offs. A licensed plumber can test the pressure and, if it is too high, fit a pressure reducing valve so the water reaches your taps more gently. Ask to see the reading before and after.
If the noise centres on your storage heater, or the heater has started making new sounds, go through the water heater warning signs before you keep relying on it.
Simple checks first
These need no tools and take about ten minutes.
- Find the trigger. Run each tap and appliance in turn. Note which one causes the bang and whether it happens on hot, cold or both.
- Close it slowly. Ease the lever shut over a second or two. If the bang softens, closing speed is part of the cause.
- Check visible clips. Look under the kitchen sink and the basin. A pipe that shifts easily by hand can slap the wall when a surge hits. Do not bend or force it.
- Look at the tap. A tap that drips, whistles or turns stiffly may have a worn part. The leaking tap fix guide explains the usual repair.
- Watch the heater. Note whether the noise only comes with hot water, and look for drips around the heater pipes from a distance.
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Compare plumbersOld pipes and corrosion
If your home still has older galvanised iron pipes, age tends to show at the joints. PUB advises checking pipes and fittings regularly, replacing faulty or corroded fittings promptly, and replacing unlined galvanised iron pipes with cement-lined ductile iron or copper pipes.
HDB notes that leaking pipe joints can come from usage and deterioration over time, or from pipes being hit by objects.
Corroded pipes are not always noisy, so rust marks or crusting at fittings are also worth a closer look. Replacing pipes buried in walls is a bigger job. The guide to concealed pipe replacement cost explains what shapes the quote, and PPR vs copper pipes compares two materials you may be offered.
When to call a plumber
Call a licensed plumber if the bangs continue after you close taps slowly, if a joint drips or sprays, or if you see damp patches, bubbling paint or stains on a wall or on the ceiling below. HDB advises checking pipe fittings regularly for leakages and engaging a licensed contractor where repairs are needed. If there is a leak, HDB says to shut the stopcock at the PUB water sub-meter to cut the water supply. For other red flags, see signs you need a plumber.
Questions
Is water hammer dangerous?
Not right away, but do not ignore it. Each bang sends a pressure surge through your pipes, and repeated surges can stress joints, clips and tap connections over time. An occasional soft knock is mostly a nuisance. Loud bangs every time a tap closes, or bangs that come with a new drip, deserve a licensed plumber's visit.
Why do pipes knock at night?
Usually because a valve shuts while the house is quiet enough to hear it. A washing machine or dishwasher on a timer, or a toilet cistern refilling after a late flush, can cause a knock. Hot pipes ticking as they cool after evening showers is another cause. Note the time and the room so your plumber can trace it.
Can a water hammer arrestor be fitted in an HDB flat?
Ask a licensed plumber, because an arrestor goes on the water supply line and is not a DIY job. PUB requires regulated water service plumbing works to be done by PUB Licensed Plumbers, apart from the simple works a handyman may do. The plumber can also tell you whether slower taps, firmer clips or a pressure reducing valve would fix the noise.
Why does my tap whistle?
Most often, a worn washer or cartridge, or a valve that is only partly open, is forcing water through a narrow gap. Check that the valve under the basin is fully open. If the whistle continues, the tap needs repair or replacement, and the leaking tap guide above covers the usual parts. High pressure can make the whistling louder.
Is a humming pipe a leak?
Not usually. A hum is more often linked to high pressure, a partly closed valve or a pump running nearby. To rule out a leak, close every tap and watch the water meter. PUB suggests daily or weekly meter readings to spot leaks. If the meter moves when nothing is running, call a licensed plumber.
Who fixes pipes inside the wall?
A PUB Licensed Plumber. PUB says regulated water service and sanitary plumbing works must be done by PUB Licensed Plumbers, and since 2018 it has been an offence to engage a plumber not licensed by PUB for regulated works. A handyman may do simple works such as installing or replacing a washbasin or sink and its bottle trap.
Practical guidance for planning a home job in Singapore. Company prices come from the HomezyPro directory, each linked to its source; rules and safety points link to the agency or manufacturer that sets them. This is not a site inspection, a quote or professional advice for your home.
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