How to Inspect Water Supply Pipes for Leaks in a Flat or Apartment Building

In an apartment building much of the supply pipework is hidden in walls, floors and shared shafts, and the first sign of a leak is often a damp patch some distance from the fault. Work through the checks below in order: they move from what you can see to what you can only test.

How water reaches your flat, and where pipes can leak

Many Dhaka apartment buildings pump water from an underground reservoir up a rising main to a roof tank, then let gravity carry it down risers (vertical pipes, usually in a service shaft) to a branch on each floor. Each flat's branch typically has an isolation valve, after which concealed pipes run through walls and floor screed to the bathrooms and kitchen. Pressure is highest on the lowest floors, roughly 1 bar per 10 metres of height, so the same defect leaks harder lower down; for pressure problems, see our guide to low water pressure.

Knowing this route matters because it splits responsibility. A leak upstream of your flat's isolation valve, on the riser or the branch, usually concerns the building and is for the committee or caretaker to deal with; a leak downstream of it is normally inside your flat. Your first inspection goal is to find out which side of that valve the water is escaping from.

Warning signs of a leaking supply pipe

Supply leaks differ from drainage leaks in one useful way: the pipe is always full and under pressure, so the leak does not wait for someone to use a fixture. Look out for:

• A damp patch that stays wet or keeps spreading through the day and night, even when nobody has used the bathroom or kitchen.
• Yellow, brown or dark staining, or paint and plaster that bubbles or peels; WaterSafe lists these as typical signs of water inside a wall.^[2]
• A musty smell or mould along pipe routes. The US Environmental Protection Agency (EPA) notes that mould can grow unseen inside walls around leaking or condensing pipes.^[3]
• A faint hiss or trickle inside the wall when every tap is shut; listening quietly near suspect areas is one of the first checks WaterSafe suggests.^[2]
• A meter that keeps turning, or a bill that rises with no change in use.^[2]
• In a tank-fed building, a pump that runs more often or a roof tank that empties faster at night.
• In older galvanised iron (GI) pipework, brown water after a few days unused, falling flow at every tap, or rust crust on joints.^[4]

Is it a leak or condensation?

During the monsoon, cold-water pipes and the walls around them can sweat. EPA describes condensation as a sign of high humidity and recommends insulating cold-water pipes.^[3] Condensation forms evenly along a cold surface and comes and goes with the weather; a leak starts at one joint and persists in dry air. Wipe the pipe dry, wrap dry tissue round each joint and check after an hour: a wet band at one fitting means a leak, a uniformly damp pipe means condensation.

Why supply pipes fail

• Corrosion of GI pipe. Galvanised steel rusts from the inside, narrowing the bore and thinning the wall; InspectAPedia notes that threaded joints usually fail first because the wall is thinnest there.^[4]
• Mixed metals. Where steel meets copper or brass without an insulating (dielectric) fitting, galvanic corrosion can eat into the joint.^[4]
• Badly made PPR (polypropylene random copolymer) heat-fused joints; one fitting maker warns that cracked pipe gives leaking joints, dirty pipe will not form proper beads, and the pipe must not be twisted as it goes in.^[5]
• Hurried uPVC or CPVC solvent joints, with the pipe not pushed fully home or the system filled before the cement cured.
• Renovation damage: a nail, screw or drill through a concealed pipe, or a pipe cracked while nearby tiles were broken out.

Tools you need, and what instruments can and cannot show

A basic inspection needs very little:

• A bright torch, dry tissue or toilet paper, and a few dry cloths.
• A pencil, a phone camera and a notebook to mark, date and record stains and readings.
• Access to your flat's main isolation valve and, if your flat has one, its water meter.
• Optionally, a pin or pinless moisture meter for comparing readings across a wall.
• A stable step ladder for ceilings; never stand on fittings or furniture.

Moisture meters and thermal cameras

A moisture meter reads only the surface layer near its tip, and on plaster or brick its numbers are comparisons, not true moisture contents. Take readings in a grid across the damp area and compare them with a dry part of the same wall; the highest readings usually sit below or beside the leak.

A thermal (infrared) camera shows surface temperature, not water. Fluke, a maker of these cameras, explains that wet areas often appear as cooler patches because evaporation cools them, but only under the right conditions, and that confirming the source may still need invasive work.^[7] Fluke adds that a bigger temperature difference gives clearer images, which air-conditioning or running cooler water through the pipe can help create.^[7] Treat a thermal image as a map of where to look next, not as proof.

Step by step: inspecting the supply pipes in your flat

Work through these steps in order. Each one narrows the search, and the notes you keep will save time if a plumber or the committee gets involved.

1. Record what you can see. Photograph each damp patch, mark its edge in pencil with the date and time, and note whether the wall carries pipes to a bathroom or kitchen.
2. Make electrics safe. If water is near sockets, switches, light fittings or a water heater, switch that circuit off at the breaker before touching anything.
3. Find and try your flat's main isolation valve. Check that it turns and closes fully; a valve that will not shut makes every later test unreliable and needs a plumber.
4. Inspect all exposed pipework: under sinks, behind toilets, at the water heater and on verandas. At each joint and valve, look for drips, white or green crust, rust stains and tissue that turns wet.
5. If your flat has its own meter, do a meter test. Turn off every tap and appliance, wait about 30 minutes for cisterns to refill, read the meter including the red digits, then use no water for three to six hours and read it again; a higher second reading suggests a leak.^[1] EPA describes a shorter version: compare readings before and after a two-hour period with no water use.^[9] In tank-fed buildings the WASA meter usually sits before the underground reservoir, so it cannot test the pipes inside your flat.
6. Narrow it down. If the meter moved, close your flat's main valve and repeat the test, as United Utilities advises; if the meter still moves, the leak is between the meter and the valve.^[1]
7. Without a meter, use the valve itself: close the flat's main valve for several hours, ideally overnight. If a hiss stops and a damp patch starts to dry, the leak is inside your flat; if not, suspect a shared pipe, the flat above or rain.
8. Isolate fittings one at a time. With the main valve open again, close the small valve feeding each toilet cistern or tap in turn. If the sign stops with one of them closed, that fitting is at fault; see how to find and fix bathroom leaks.
9. Trace concealed routes. Pipes usually run straight up, down or across from each tap outlet; mark likely routes lightly and take moisture-meter readings along them.
10. At a quiet time, with every tap off, listen with an ear close to the wall along the marked routes.^[2]
11. Write up the date, tests, readings, photographs and your conclusion, and share them with neighbours and the committee if a riser or shared wall is involved.

Risers, shafts and shared pipes

A leak on a riser or in a service shaft often shows on several floors at once, along the same vertical line, and does not stop when any one flat closes its valve. Report it to the building committee or caretaker with your notes and photographs rather than waiting for a neighbour to notice. Who pays usually depends on whether the fault is before or after a flat's own valve; the flat maintenance guide explains how to agree this before a dispute starts.

Leaks matter for water quality as well as damage. Research on intermittent supplies found that any crack or hole that lets water out can also let contaminated water in while the pipe is depressurised, and that dirt drawn in during those periods is flushed into homes when supply returns.^[8] Where tanks run dry or supply stops for hours, check supply pipes near drains and floor traps with extra care.

What failure looks like in different pipe materials

You do not need to know every material in detail to inspect pipes, but you should know what failure looks like in the ones you can see. For choosing replacements, see how to choose suitable pipe materials.

What a plumber's pressure test can show

When the leak is inside the flat but cannot be pinned down, a plumber can isolate a section, pressurise it and watch a gauge: if the pressure falls with no water in use, that section leaks, and testing smaller sections narrows the search before any tile is broken. WaterSafe describes a simpler version: with all fixtures off, fit a gauge to an accessible tap and see whether the pressure drops over a few hours.^[2]

Under the UK water fittings regulations, for example, a system must withstand at least 1.5 times its maximum working pressure, and United Utilities expects a competent tester to record the pipe material and size, test pressure, start and end times and result.^[6] Bangladesh rules may differ, but asking for those details in writing is sensible. A remade PPR joint should be pressure-tested once it has cooled.^[5]

A routine to prevent supply-pipe leaks

The most expensive pipe leaks run unnoticed for months. A light routine catches them early.

For a whole-building checklist that also covers drains, tanks and pumps, see the plumbing inspection checklist; for early warnings across the whole system, see how to spot plumbing problems early.

Common mistakes and troubleshooting

• Breaking the wall at the centre of the stain. Water travels along pipes and down through plaster, so the leak is often above or beside the patch; trace and test first.
• Taking condensation for a leak, or a leak for condensation. Do the dry-tissue test on each joint before deciding.^[3]
• Relying on one thermal image. Without a temperature difference it can miss a leak, and it can show cool patches that are not wet.^[7]
• Wrapping a weeping joint in tape or epoxy putty and calling it fixed. That is a stopgap only.
• Forcing a stiff, corroded GI valve or union with a long spanner, which can snap a thinned thread.
• Meter moves but nothing is visible: repeat the test with the flat's main valve closed, then check cistern overflows and water-heater relief pipes before suspecting concealed pipes.
• Damp only after heavy rain: the roof, an outside wall or a window is a more likely cause than a supply pipe; see how to prevent damp walls and seepage.

When to call a plumber, and repair versus replacement

Call a plumber when the leak is in a concealed pipe, when it is on or near a riser, when the valve test cannot separate inside from outside, or when water is damaging the flat below. WaterSafe also advises calling one if you cannot locate the leak after visual checks, listening and meter tests, or if the damage keeps getting worse.^[2]

A single weeping joint on otherwise sound pipe can usually be remade. Repeated leaks along old GI pipework, heavy rust at the threads and falling flow suggest that the pipe itself is near the end of its life, which InspectAPedia puts at roughly 40 to 60 years for galvanised steel.^[4] Whether to patch, replace a section or re-pipe is covered in when to repair or replace a damaged water pipe.

What drives the cost of finding and fixing a pipe leak

We could not find reliable published prices for leak detection or pipe repair in Bangladesh, so this guide gives none. The main cost drivers are:

• Access: an exposed joint under a sink is quick; a concealed pipe means breaking tiles and plaster, then making good.
• Locating the leak: a plumber's isolation or pressure test, or an instrument survey, adds time but can save opening the wrong wall.
• Scope: remaking one joint costs far less than replacing a run of corroded pipe.
• Shared pipework: riser repairs may need several flats to cooperate and are usually a building cost.
• Damage elsewhere: ceilings, paint and furniture in the flat below.

Ask for written quotes stating how the leak will be located, what will be opened, the pipe and fittings to be used and the warranty; see getting and comparing repair quotes.

Next steps

1. Today: make wet electrics safe, photograph and date any stains, and find your flat's main valve.
2. This week: inspect the exposed pipes, do the meter or valve test, and isolate fittings one at a time.
3. If the leak is before your valve or on a riser, report it to the committee in writing with your notes.
4. If it is a concealed pipe inside your flat, call a plumber and ask how they will locate it before anything is broken.
5. Get written quotes for any concealed or repeated repair.
6. Put the monthly checks in your calendar and keep your notes for next time.