Mould needs a steady supply of moisture, and in Singapore that is usually condensation, a leak or seepage, or poor ventilation. You cannot reliably tell which from a photo. Record the clues that point one way, contact whoever owns the repair if water may be coming in, and ask for a moisture assessment if the cause is unclear. Treat the mould only after the source is dealt with and the surface is dry.
Why the question matters
Condensation, a leak and poor ventilation can leave the same black or green marks, but they are fixed by different people. Cleaning or painting a surface does not stop a moisture supply, which is why returning mould points to the source. Our guide on why mould keeps coming back covers the recurrence side. This guide is about deciding what to check and who to call first.
Clues that point to condensation
These are clues, not proof.
- It forms on cold surfaces: the wall or ceiling near an aircon vent, the cold side of a window, the inside of an external wall, a wardrobe against an outer wall.
- It is worse when the aircon runs for long hours in a closed room, and eases when the room is ventilated.
- You can see water beading or running on the surface, for example on glass, metal frames or pipes.
- The damp does not follow rain, and does not trace a pipe, a slab edge or a wet patch above.
If the leak has already soaked carpet or flooring, the wet carpet guide explains the EPA drying guidance, the 48-hour question and which professionals handle each part.
Clues that point to a leak or seepage
- A stain that spreads from one point, or sits below a bathroom, kitchen or another unit.
- Damp that appears or worsens after rain, or on an external wall or the top floor.
- A patch that stays wet or keeps returning when the aircon is off and the room is dry.
- Bubbling or flaking paint, soft or powdery plaster, or tide marks, which show the material has been wet and not only stained.
- A rising water bill, or the sound of running water when nothing is in use.
Condensation and a leak can also be present together, for example a leaking pipe in a room that is also cold and sealed. Do not assume it is one or the other.
What to record
Take one wide and one close photo from the same spot, with the date, and repeat every few days. Note the room and surface, when it appeared, whether it follows rain or the aircon schedule, whether it returns after cleaning, and any known leak, aircon fault or recent works above or beside it. These notes help whoever inspects it, and they matter if you need to raise it with a landlord, the MCST or a neighbour.
Who to contact first
- Water may be coming in, or a pipe may be involved. Contact the party that owns the repair: a licensed plumber for a pipe in your own unit, your landlord if you rent, the MCST or managing agent in a condo, or the Town Council for the roof of an HDB block. For a leak from the unit above, see ceiling leak from the flat above: who pays and what to do first.
- Aircon dripping or a blocked drain line. An aircon servicing contractor. See how to get rid of mould in your aircon.
- No sign of a leak and the mould keeps returning. A moisture assessment can narrow down where to look next. See mould inspection in Singapore.
- Curtains near a damp window or wall. Mouldy curtains are a fabric-care question and a moisture-source question. The curtain mould guide covers care labels, backing types and checking the window area.
- An office or commercial premises. Building management for services and the structure, and the aircon contractor for tenant units. See the office mould planning guide.
What a moisture assessment can and cannot tell you
Four Solutions describes its assessment as using moisture meters, thermal imaging and UV inspection. A moisture meter gives a reading at the point tested. Thermal imaging can show temperature differences consistent with condensation or a moisture pathway. UV is a visual aid. None of them confirms what is concealed in a wall or above a ceiling, so the result is read together with what is visible and the history of the area. Where the cause is a leak, a plumber or building consultant may still need to test the pipe or structure. Four Solutions does not repair leaks, waterproof floors or service aircon.
Treat the mould after the source is dealt with
The US EPA says moisture control is the key to mould control, and that a water problem must be fixed before a cleanup can be considered finished. For wet surfaces it advises against painting or sealing until the material is dry inside. The order that works is: identify the source, fix it, let the surface dry and confirm it, then remove the mould and finish the surface. The mould removal page explains what treatment includes, and the written quote confirms the areas, the work and any warranty.
WhatsApp photos and your notes and we will tell you what we can assess.
Sources: US EPA, A Brief Guide to Mold, Moisture and Your Home and Mold Remediation in Schools and Commercial Buildings, chapter 3; BCA's guide on water seepage; HDB on ceiling leaks. Inspection methods are from Four Solutions' own service pages. This guide is general information, not a diagnosis. Checked 13 October 2026.
Condensation or leak FAQs
Can I tell condensation from a leak by looking at a photo?
Not reliably. A photo shows where mould is, not where the water comes from. Patterns can point one way, but the source is confirmed by checking moisture on site and, where needed, by a plumber or building consultant testing the pipes or structure.
Does mould in the corner of an external wall mean a leak?
Not necessarily. External walls can be cold enough to collect condensation, and they can also let water seep in. Check whether the damp follows rain, whether the paint is bubbling, and whether it is worse in the corner or across the wall face, then have it assessed.
The damp patch is under another unit. Is it condensation?
A patch under a bathroom or another unit is more consistent with a leak. See our guide on who pays and what to do first for a ceiling leak from the flat above.
Who should I contact first, a mould company or a plumber?
If water is actively dripping or a pipe may be involved, contact the party that owns the repair first: the plumber, your landlord, the MCST or the Town Council. If there is no sign of a leak and the mould keeps returning, a moisture assessment can help decide which direction to look.
When should the mould be treated?
After the source is fixed and the surface has dried. Treating mould while the moisture is still being supplied is likely to give only a temporary result.
Does Four Solutions fix leaks?
No. It assesses moisture, treats mould and can give a written assessment of its findings. Leaks, waterproofing and aircon repairs are done by other contractors.