Why Your Mould Keeps Coming Back (and Where the Water Is Coming From)

• Mould is not a stain problem. It is a water problem, and the water is still there.
• The state health guidance puts one rule first: control the moisture, or it comes back. Cleaning is the symptom, not the cure.
• Where it shows tells you more than how much of it there is, and some places are telling you about the building rather than the surface.
• Bleach changes how a surface looks. It does not change why it is wet, which is why the same corner is back in six weeks.
• And there is a point where this stops being a cleaning job at all, which is the most useful thing anybody can tell you.

You cleaned it. You cleaned it properly, with the window open and a decent cloth, and for a while the corner looked fixed. Now it is back, and if this is the third spring in a row, you are probably wondering what you are doing wrong. Here is the answer, and it is a kind one: nothing. You have been treating the symptom instead of the water. Once you find the water, the cleaning stops being a seasonal chore, and finding it is a job you can start today.

The one rule, and it is the government’s first step

Start with the sentence the Victorian health authorities put first, because it is the whole article: the best way to control mould is to control moisture, so the sources of moisture need to be found and removed or controlled, or the problem is likely to reoccur.

Then the second sentence, which is just as useful: mould will only grow in damp, unventilated rooms. Two conditions, and only one of them can be fixed with a cloth. You cannot clean a room into being dry. You can only make it dry, and the room will do the rest.

That reframes the whole situation. A household that has cleaned the same corner three winters running has not failed at cleaning. It has been doing the right job on the wrong problem, and it has been doing it in a climate that is very good at the wrong problem. A Melbourne winter is a closed-up season: the windows stay shut, the heating goes on, the washing dries inside, and every room gets a little more water in the air than it can get rid of. That is the machine that keeps feeding the corner, which is the point the site’s The science behind Melbourne’s unpredictable climate: what’s really going on? makes from the weather side.

Where the water actually comes from

Walk your own house with this list in your head, because almost every source is ordinary and none of them is exotic.

The bathroom is first, and it is the wettest room in the house. A hot shower puts a surprising amount of water into the air, and the fix is usually airflow rather than repair: a room that gets shut up straight after a shower keeps every drop of that steam, and it condenses on the first cool surface it finds.

And cool surfaces are where you will see it. Windows, the frames, the reveals at the sides of the glass, external wall corners, the back of a wardrobe standing against an outside wall, the wall behind a bed headboard. Water in the air goes to the coldest place it can, which is why the same corner of the same room shows up every year.

The roof and the plumbing are the two the guidance names explicitly, including damaged pipes and drains, and the instruction that comes with them is short: call a plumber. That is not a cleaning matter and no amount of scrubbing will settle it.

The laundry and the drying are the quiet one. A load of washing dried indoors puts water into the room that then gets closed up, and a household that does it every week is running a small humidifier on purpose.

And then everything small that puts water into one room’s air. The kettle boiled under a low cupboard. The aquarium. The plants. The slow drip under the kitchen sink that nobody has dealt with, quietly adding to the tally every day.

The reader is looking for one combination: the room that is wet and shut. Wet and open is fine. Dry and shut is fine. Wet and shut is where mould lives.

Where it shows, and what each place is telling you

Where it turns up is more informative than how much of it there is, so read the spots like a clue, not a stain.

The shower screen and the silicone line. That reading is simple: moisture sitting on a surface that never gets to dry, because the screen faces the water and the bathroom faces the dark. The answer is airflow and wiping it down, not harder scrubbing.

Grout, and the wall behind the shower. When it keeps returning here, the water may be getting behind the surface rather than sitting on it, which is a different problem with a different fix.

Windows, frames and reveals. That is condensation, which is about the air in the room rather than the window itself, so the cure lives in ventilation and heating rather than in a spray bottle.

The ceiling, especially in the coldest room, and the ceiling of the room under a bathroom. Look up before you look anywhere else, because a ceiling is either a cold surface or a sign that water is coming from above.

The back of the wardrobe, the wall behind a bed, the base of a mattress. An outside wall with no air moving past it is a condensation machine, and furniture pressed tight against it gives the moisture nowhere to go.

Boxes, shoes, leather and paper in a cupboard or a garage. Slow, long-running damp that you may never have seen, and one that tends to be discovered at the moment something valuable is ruined.

And one place people miss because it is hidden in plain sight: the panel or the void around a bath or a shower recess. If there is a way in, it is worth a look with a torch.

What to clean, what to throw out, and what not to do

The method, kept simple on purpose, because none of it needs a special product.

Hard surfaces first. Household detergent or white vinegar is often enough. Use a microfibre cloth, and as you work, rinse the cloth in a separate container of clean water rather than rinsing it under the tap that the mould is sitting next to. That one habit is the difference between removing it and moving it around. Give the cleaner a moment to work, avoid getting the area too wet, and dry it afterwards, because a cleaned surface that stays damp is a surface that starts the clock again.

Soft things next. Clothing, bedding and soft fabric items, including soft toys, can go through a washing machine on a hot cycle. Wash the cleaning cloths separately. A couple of honest caveats from the guidance: bedding that has been mouldy for weeks may not be salvageable, and soft furnishings that cannot be machine washed need to be cleaned professionally or thrown out. There is no third option that a cloth will provide.

And the things that are not worth cleaning at all. The guidance names cardboard boxes and mattresses, and it is right. Materials that hold water in their core never really come clean.

Then the safety line, which is the one that matters most: never mix bleach with ammonia, acids or other cleaners, because doing so can release hazardous fumes. That is the government’s own warning, and the sensible version of it is simple: do not mix cleaning products at all.

And the honest verdict on bleach itself, kept as careful as it needs to be: bleach changes how a surface looks. It does not change why it is wet. That is why the same corner is back in six weeks, and why a bottle of anything will not do the work that a dry room does. The site’s Boost productivity and mood with a deep cleaned space shows what a proper clean covers when the room is ready for it. First, make the room ready.

When it is not a cleaning job at all

Here is the section that will save some readers real money, and it is the part no product page will ever tell you.

Three situations stop being about cleaning. The first is scale: if it covers a large area, or it keeps regrowing after you have cleaned it, the guidance’s own instruction is to consult a mould remediation professional. That is not a sales line from anyone. It is the point where the surface is no longer the story.

The second is a leak. If there is plumbing or roofing water getting in, the instruction is to call a plumber, full stop. Water that keeps arriving will keep bringing the mould with it, and the fastest clean in the world cannot outrun a drip.

The third is the building’s own fabric: a wall with no visible cause, a ceiling that comes back, a cupboard that is damp even in summer. Those are questions about the structure of the house, and the state health guidance points to two places that can help, the environmental health section of your local council and an occupational hygienist. Both exist, both are worth knowing about, and which one fits your situation is a question to ask rather than guess.

One line worth keeping, because it cuts through all of it: a cleaner who says “this one is not mine” is worth listening to. That is the standard a residential and commercial cleaning company working across Melbourne’s west works to, and it is the right instinct for a household too.

The four habits that stop it coming back

None of this is difficult. It is just boring, which is why the same bathroom gets cleaned every spring.

Airflow first, because it does most of the work. The guidance’s simplest drying advice is to open doors and windows and air the house properly, and the practical version for a bathroom is the fan on and the door open after a shower, rather than the fan on and the door shut.

Dryness second. Wipe or squeegee the wet surfaces, hang the towels where they can dry, and keep the washing out of rooms that then get closed up.

Furniture placement third. Nothing tight against an outside wall. A gap behind the wardrobe, a gap behind the bed, air under the mattress. You are not rearranging the house, you are giving the air a route.

And the water itself, fourth, which is the one that decides whether next spring is the same story. The dripping tap, the leaking gutter, the cracked tile, the seal around the bath. Fix the water and the mould loses its supply.

Before you clean it again

The compressed version, for the cupboard door where the cloth lives.

Find the water before you buy anything. Air the room and dry the surfaces. Clean hard surfaces with detergent or white vinegar and a cloth you rinse in clean water as you go. Wash what can be washed hot, throw out what cannot be cleaned, and never mix bleach with other cleaners. Write down where it came back, because the pattern is the diagnosis. And if it is large, or it keeps returning, stop treating it as a cleaning problem and get somebody to look at the moisture itself.

The mould is what the water did. The water is the only thing worth chasing.

Sources consulted: Victorian Government Better Health Channel information on mould removal at home.