Hong Kong’s 2026 Water Seepage Investigation Procedures: How Infrared Thermography and Electronic Moisture Meters Help Trace the Source
When stains, blistering paint, discoloured plaster or a musty smell appear on a wall, many Hong Kong property owners immediately suspect leakage from the flat above or rainwater entering through an aluminium window. Yet the same visible symptom may be caused by a water supply pipe, a drainage pipe, defective bathroom waterproofing, an external wall crack, a window-frame joint or even surface condensation. Starting repair works before identifying the likely source may fail to solve the problem and may cover up evidence that would otherwise help trace the water path.
On 16 July 2026, the Joint Office formed by the Food and Environmental Hygiene Department and the Buildings Department fully implemented new procedures for investigating water seepage in private buildings. At Stage I, infrared thermography is now used together with an electronic moisture meter to assess seepage conditions and make a preliminary judgement about the possible source. This change highlights a sound principle for any seepage case: evidence should be collected and compared before repair decisions are made.
This guide explains the new procedures from an owner’s perspective, how infrared thermography and electronic moisture meters work, what these instruments cannot prove on their own, the common sources of water seepage, and the difference between a government investigation and a privately commissioned professional assessment.
Contents
- Quick summary
- What are Hong Kong’s new water seepage investigation procedures?
- How does infrared thermography assist a seepage investigation?
- What can an electronic moisture meter measure?
- Why should the two instruments be used together?
- A water stain does not always come from upstairs
- Government procedures and private professional investigations
- What should an owner do after discovering a water stain?
- Why investigate before carrying out repair works?
- The role of an EJW digital water seepage investigation report
- Common misunderstandings
- Frequently asked questions
- Conclusion
- References
Quick Summary
| Key point | What property owners should know |
|---|---|
| Effective date | The Joint Office fully implemented its new procedures for investigating water seepage in private buildings on 16 July 2026. |
| Stage I assessment | Infrared thermography is used together with an electronic moisture meter to assess seepage conditions and preliminarily identify the possible source. |
| Purpose of thermography | It compares the surface-temperature pattern at a suspected area with nearby dry reference areas to identify anomalies and the extent of the affected area. |
| Purpose of a moisture meter | It provides moisture-related readings at selected points on walls, ceilings or other materials so that their distribution and changes can be compared. |
| Important limitation | A single thermal image or moisture reading is generally insufficient to prove a source. Location, timing, environmental conditions and other tests must also be considered. |
| Government and private services | The Joint Office follows a government investigation and enforcement process. A private investigation and digital report can help an owner understand site conditions but do not replace a government finding or statutory decision. |
What Are Hong Kong’s New Water Seepage Investigation Procedures?
According to the Government, the Joint Office applies the new procedures to reports concerning water seepage in private buildings received on or after 16 July 2026. Cases received before that date continue to be handled under the previous procedures.
A principal change is the simultaneous use of infrared thermography and an electronic moisture meter at Stage I. Temperature and moisture patterns at the affected location can therefore be examined at an earlier point in the process. Where there is reason to believe that the seepage is caused by an upper-floor unit, the Joint Office may issue a Notification Letter requiring its owner to arrange inspection and testing and complete repair works within 28 calendar days.
If seepage persists after the specified period, the Joint Office may conduct the Stage II basic investigation and Stage III professional investigation concurrently. Only after the evidence confirms that the source is an upper-floor unit and the relevant public-health nuisance is established will the authority proceed under the Public Health and Municipal Services Ordinance (Cap. 132), as applicable to the case.
A Notification Letter is not the same as completion of every confirmatory step, and the presence of a water stain does not automatically prove that the flat above is responsible. Each case must still be assessed using site information, instrument findings and any necessary follow-up tests.
What are the new procedures intended to improve?
Under the previous workflow, complex cases could take time to progress through the investigation stages. Introducing non-destructive technology at Stage I is intended to identify suspicious areas earlier and encourage the relevant owners to inspect, communicate and arrange repairs sooner.
However, a faster preliminary assessment does not mean that one instrument can provide an instant and final answer. Water can travel along a slab, wall cavity, window joint or the back of a finish, so the visible stain may not be the point of entry. Depending on the suspected source and site conditions, follow-up work may still involve moisture monitoring, colour-water testing, ponding or spray testing, reversible pressure testing of water supply pipes, microwave tomography or another suitable method.
How Does Infrared Thermography Assist a Seepage Investigation?
Infrared thermography does not directly “see water inside a wall”. It detects infrared radiation emitted from a surface and translates differences in surface temperature into an image that can be compared. A damp building material may absorb, release or lose heat through evaporation differently from a nearby dry area, creating an unusual thermal pattern.
An investigator can compare the suspected seepage location with surrounding dry reference areas and study the shape, direction and extent of the anomaly. For example, a pattern spreading from above a window frame may support a different hypothesis from one extending downwards from the centre of a ceiling. These patterns must nevertheless be interpreted alongside the building layout, materials and other measurements.
Main advantages of infrared thermography
- Non-destructive assessment: an initial scan will normally not require a wall or ceiling to be opened.
- Non-contact operation: the method can assist with areas that are difficult to reach directly.
- Pattern mapping: it helps show the extent of an anomaly rather than only one measurement point.
- Useful records: thermal images can be organised with normal photographs, locations and moisture readings.
Why can a thermal image not provide the conclusion on its own?
Moisture is only one possible cause of a surface-temperature difference. Sunlight, air-conditioning, hot or cold pipes, reflective metal, furniture, different finishes and recent weather conditions can all alter the image. A professional assessment should therefore record the inspection time, indoor and outdoor conditions, surface materials and reference areas before comparing the thermal pattern with other findings.
The colours in a thermogram represent relative temperatures. A blue, red or otherwise contrasting area does not, by itself, establish the presence of water, the severity of leakage or the party responsible.
What Can an Electronic Moisture Meter Measure?
An electronic moisture meter collects moisture-related readings from a wall, ceiling or other building surface. The useful part of an investigation is generally not a single number. It is the systematic comparison of the suspected area, its boundary and dry reference points on the same or a similar material.
If readings gradually reduce away from one area, or repeated measurements show a consistent change over time, the information may help define the affected zone and establish a trend. Nevertheless, readings can be influenced by the instrument and mode used, material thickness, concealed metal, surface salts and finishes. A percentage adopted within one official workflow should not be mechanically treated as a universal private-testing threshold for every instrument and building material.
What other information should be considered with moisture readings?
- Whether the stain appears after rain, after water use or continuously
- The relative positions of walls, ceilings, windows and pipes
- Reference readings taken on dry areas of the same material
- Air-conditioning, ventilation, indoor humidity and condensation
- Previous repairs, repainting and waterproofing works
Why Should Infrared Thermography and an Electronic Moisture Meter Be Used Together?
The two instruments provide different types of evidence. Thermography is useful for visualising surface-temperature patterns and the extent of an anomaly. A moisture meter provides comparable readings at selected points. When the location, shape and changes shown by both sets of information are consistent, an investigator has a stronger basis for deciding whether a targeted follow-up test is required.
| Assessment method | Main information provided | What it cannot prove on its own |
|---|---|---|
| Infrared thermography | Surface-temperature differences, anomalous areas and distribution patterns | Colour alone cannot prove that water is present or identify the responsible unit |
| Electronic moisture meter | Moisture-related readings and relative changes at selected locations | A single reading cannot establish the route by which water entered |
| Site observations and records | Timing of stains, odour, surface condition, and locations of windows and pipes | Visual inspection may not reveal concealed water paths or moisture within materials |
| Targeted testing | Further evidence for a specific hypothesis, such as colour-water, spray or pressure testing | Other possible sources outside the test scope may still require investigation |
The value of an investigation is not measured by the number of instruments listed. What matters is whether each test addresses a clear hypothesis, whether the findings support one another, and whether the report states the locations and conditions that could not be assessed.
A Water Stain Does Not Always Come from Upstairs: Common Sources of Seepage
The Buildings Department identifies common causes including defective drainage or water supply pipes, defective floor-slab waterproofing or bathtub sealants, and rainwater entering through a roof, podium, balcony, external wall or window. Owners should therefore avoid assigning responsibility to a particular flat before supporting evidence has been collected.
| Possible source | Common clues | Possible investigation direction |
|---|---|---|
| Water supply pipe | Dampness may be continuous or become more apparent during water use, without a clear relationship to rain | Review the pipe route and usage pattern, and arrange an appropriate pressure-related test where necessary |
| Drainage pipe or sanitary fitting | The condition may change after drainage occurs in an upper or adjacent location | Inspect drainage connections and fittings, and consider a colour-water test where suitable |
| Bathroom or floor waterproofing | The stain may correspond with showering, washing or prolonged water on a floor | Consider ponding, spray or another targeted test under suitable site conditions |
| Rainwater through an external wall or window | The problem may become more obvious after heavy rain, a particular wind direction or a typhoon | Inspect wall cracks, window-frame joints, sealants, drainage points and the likely rainwater path |
| Surface condensation | It may occur in air-conditioned, humid or poorly ventilated conditions without an external water source | Compare indoor humidity, surface temperature, ventilation and the usage pattern |
Where the problem is concentrated around a window or occurs only after wind-driven rain, owners may refer to EJW’s aluminium window leakage and waterproofing services and its guide to aluminium window waterproofing in Hong Kong for further information about frame joints, sealants and external-wall interfaces.
What Is the Difference Between a Government Procedure and a Private Professional Investigation?
The Joint Office procedures form a government administrative and enforcement process for handling reports of water seepage in private buildings. The authority determines its scope and any follow-up action according to the law, evidence and circumstances of the case. A private investigation is commissioned by an owner, occupier or another relevant party, usually to understand conditions earlier, narrow down the possibilities, plan repair works or support communication.
| Item | Joint Office investigation | Private professional investigation |
|---|---|---|
| Nature | A government process for handling seepage reports and the relevant public-health nuisance | A site investigation commissioned by an owner or occupier |
| Scope | Determined by government powers, legislation and case circumstances | Determined by the engagement, accessible areas and available testing conditions |
| Use of findings | Used by the Joint Office for decisions and follow-up under its procedures | Helps the client understand conditions, plan works and retain a record |
| Legal effect | Relevant decisions are made by the government authorities under the applicable law and procedures | A private report is not a government notice, statutory determination or legal allocation of liability |
Not every type of seepage falls within the Joint Office’s enforcement action under Cap. 132. The Buildings Department explains that, under normal circumstances, rainwater entering through a roof, podium, balcony, external wall or window, as well as seepage caused by a defective water supply pipe, does not constitute the type of public-health nuisance for which the Joint Office takes enforcement action under that Ordinance. Owners facing these situations may still need to arrange an appropriate professional inspection and repair themselves.
What Should an Owner Do After Discovering a Water Stain?
Step 1: Preserve an undisturbed record
Take wide and close-up photographs and record the date, time, weather, wind direction, use of air-conditioning and whether the affected area is expanding. Unless immediate safety work is required, avoid repainting or completely covering the stain before an initial assessment.
Step 2: Establish the relationship between timing and events
Observe whether the condition appears only after heavy rain, after water use upstairs, when a particular pipe is in operation, or after prolonged air-conditioning. A consistent timing pattern can be more useful for narrowing down possible sources than a photograph taken on one occasion.
Step 3: Address immediate safety risks
If water is close to a switch, light fitting or appliance, do not touch damp electrical equipment. Where it is safe to do so, isolate the relevant power supply and seek assistance from a qualified person. Loose or bulging ceiling plaster should also be isolated if there is a risk of falling material.
Step 4: Communicate with building management and relevant neighbours
Where a common external wall, roof, podium or another flat may be involved, notify the property management company and ask whether recent pipe incidents or maintenance works have been recorded. Describe any source as “suspected” rather than assigning responsibility before it has been established.
Step 5: Select an investigation method that matches the suspected source
Rainwater around a window, defective bathroom waterproofing, a drainage pipe and a water supply pipe require different testing approaches. A professional investigator should first develop reasonable hypotheses and then select suitable instruments and tests, rather than applying exactly the same procedure to every case.
Why Investigate Before Carrying Out Repair Works?
A common mistake is to apply waterproofing material only where the stain is visible or to reseal every joint before the source has been assessed. Water may travel through a slab, cavity, window-frame joint or behind a finish. The internal exit point and the external entry point may therefore be some distance apart.
The purpose of investigation is to eliminate possible sources methodically and align the repair scope with the available evidence. If no obvious evidence of active seepage is found within the inspected scope, a professional record should state that finding honestly instead of describing an uncertain condition as a confirmed defect merely to promote repair works.
Where evidence indicates a problem, the location, observed condition and basis of assessment should be clearly explained. Where the evidence is not yet sufficient, the inspection scope, limitations and recommended monitoring should also be stated so that the client does not undertake unnecessary work before the cause is understood.
The Role of an EJW Digital Water Seepage Investigation Report
Within the agreed inspection scope, EJW can organise site photographs, thermal images, material moisture readings, inspection locations, observations and recommended next steps into a digital water seepage investigation report for the client. Its value lies in placing different information within the same location and time context, enabling the owner to understand how the assessment was reached.
A clear private investigation report should state:
- The inspection date, locations and accessible scope
- Weather, surface conditions and relevant background information
- Instruments and test methods used
- Comparisons between suspected and reference areas
- What is supported by evidence, what remains unconfirmed and what has been reasonably excluded
- Whether monitoring, reinspection or further targeted testing is recommended
- The limitations of the report and interpretations that should not be made beyond its evidence
This digital report is an analytical document provided by EJW to help the client understand inspection findings and support engineering follow-up. It is not a Joint Office investigation report, a government notice, a statutory document or a legal determination of liability.
Common Misunderstandings About Water Seepage Investigations
Mistake 1: Colours in a thermal image always mean leakage
A thermal image represents differences in surface temperature. Moisture is one possible explanation, but air-conditioning, sunlight, reflective metal and variations in materials can produce temperature differences as well.
Mistake 2: A high moisture reading proves the water came from upstairs
A reading may help identify an area requiring further assessment, but the water may originate from a pipe, external wall, window or waterproofing layer. A single reading cannot allocate responsibility.
Mistake 3: The visible stain is the point where water entered
Water can travel along structural joints, material gaps and slopes. The stain may be an exit or collection point, while the actual entry point is elsewhere.
Mistake 4: The same test is suitable for every case
Rainwater at a window, drainage leakage, a water supply pipe and defective bathroom waterproofing require different approaches. Testing should be designed around the site hypothesis.
Mistake 5: A private report is the same as a government determination
A private professional report can provide useful records and analysis, but any government action is determined by the relevant authority under the applicable law, procedures and its own investigation findings.
Frequently Asked Questions
When did Hong Kong’s 2026 water seepage investigation procedures take effect?
The Joint Office fully implemented the new procedures on 16 July 2026. Cases received on or after that date are handled under the new procedures, while earlier cases continue under the previous arrangements.
Does every case immediately proceed to advanced testing?
No. Stage I first assesses the seepage condition and possible source. Whether further stages are required and which tests are suitable depend on the evidence and site conditions in the particular case.
Can infrared thermography directly see water inside a wall?
It should not be understood as directly seeing water. Thermography shows surface-temperature patterns. An investigator must compare those patterns with moisture readings, the building layout, weather and other evidence.
Does a high electronic moisture-meter reading prove leakage?
Not necessarily. A higher reading indicates that the location deserves further assessment, but readings may be affected by materials, concealed metal, surface salts and environmental conditions. Dry reference areas and other findings should be compared.
Is a stain beside a window always caused by deteriorated window seals?
No. Possible sources include the window-to-wall joint, glazing seal, drainage path, external wall crack, sill or air-conditioner opening. Surface condensation may also be involved. The timing and location must be assessed.
Will the Joint Office take enforcement action for every case of rainwater seepage?
The Buildings Department states that rainwater entering through a roof, podium, balcony, external wall or window will not, under normal circumstances, fall within the Joint Office’s enforcement action under Cap. 132. Owners may need to approach building management and arrange their own professional inspection and repair.
Should an owner repaint immediately after discovering a stain?
Unless immediate safety work is required, record the location, extent and pattern first. Covering the stain too early may remove useful evidence and does not remedy moisture within the material or an external source.
Is an EJW digital water seepage investigation report a government document?
No. It is a digital analytical document provided to the client within the inspected scope to organise findings and support follow-up communication. It is not a Joint Office report, government notice or statutory determination of liability.
Conclusion: Instruments Build Evidence; They Do Not Manufacture Certainty
By introducing infrared thermography at Stage I and using it with electronic moisture meters, Hong Kong’s 2026 procedures place greater emphasis on collecting objective information earlier and encouraging owners to address seepage more promptly.
For property owners, the most important issue is not a particular instrument or an instant answer. A sound investigation needs reference areas, location records, reasonable hypotheses, cross-checking and clearly stated limitations. Only after establishing whether seepage is present, where it may be entering and what remains unconfirmed should the repair scope be decided.
EJW provides aluminium window waterproofing inspections, water seepage investigations and related works. Through site observations, professional instruments and digital reports, EJW helps owners understand property conditions on the available evidence. Investigating first and deciding afterwards reduces the risk of ineffective repairs and unnecessary works.
References
- Hong Kong SAR Government: Government implements new procedures for investigating water seepage in private buildings
- Water Seepage Thematic Website: New procedures for investigating water seepage in private buildings
- Water Seepage Thematic Website: Use of new technologies
- Buildings Department: Frequently asked questions about water seepage
