A story from the field: the LINE message that worried Auntie Suda

Auntie Suda owns a five-storey, forty-room apartment building in a quiet soi in Don Mueang, Bangkok. Her tenants are airport staff, factory workers, university students and young families, many of whom have lived there for years. The ground floor holds eight rooms, a shared laundry room, a small lobby and a motorcycle parking area.

In late September 2026, days of heavy rain pushed the canal and the drains beyond their limits. The soi in front of the building flooded to almost half a meter. Water poured into all eight ground-floor rooms, and those tenants had to stay with relatives or friends for nearly two weeks.

When the water receded, Suda's caretaker and cleaner scrubbed away the mud, washed the floors and left the windows open. Days passed, but a damp, drain-like smell still hung over the whole ground floor. Black spots appeared on the walls. The lower panels of the built-in wardrobes had swollen. The mattresses Suda provides with each room gave off a sour, musty smell.

That night a LINE message arrived from the tenant in Room 104, a young mother with a three-year-old. "Auntie, when can we move back? But if there's still a smell or mold, I'm sorry, I think we'll have to find somewhere else. My son has allergies." Suda understood immediately. If she handled this badly she could lose every ground-floor tenant, and her building's reputation in the Facebook groups where people look for rooms around Don Mueang could suffer too.

Suda had owned the building for fifteen years and had seen heavy rain before, but never water inside the rooms for so long. She walked the ground-floor corridor with her caretaker, opening each door in turn. In some rooms the smell was faint; in others it hit her the moment the door swung open. Room 108, at the end near the drain, was the worst: a dark line of mold ran along the wall behind the bed, and the bathroom floor drain gave off a sewage smell even after it had been flushed twice. She realized that scrubbing alone was not going to be enough.

She was not alone. That week, dozens of small landlords across the district were receiving similar messages, and all of them faced the same question: how do you make a flooded room genuinely safe and fresh again, quickly, and in a way tenants will trust?

The problems landlords face after the water recedes

1. Health risks for tenants

• Leptospirosis. Floodwater from drains and canals is often contaminated. Tenants and cleaners who wade or clear mud without protection are at risk.
• Diarrhea and skin infections. Bacteria linger on bathroom floors, basins and surfaces inside rooms.
• Allergies and asthma. Mold spores from walls, wooden wardrobes and mattresses trigger symptoms in small children, older people and anyone sensitive.
• Mosquitoes and insects. Standing water around the building breeds mosquitoes and raises the risk of dengue fever.
• Stress and sleep. Moving back into a room that still smells of floodwater is unsettling. Tenants who sleep badly or worry about their children's health are far more likely to start looking for another place to live.

2. Business risks

• Tenants leaving. Several empty rooms at once means lost income every month plus the cost of finding new tenants.
• Reviews and word of mouth. Unhappy tenants often post in room-finding groups, making new prospects hesitate.
• Disputes over rent and deposits. Tenants may ask for rent reductions or early return of deposits if rooms are not ready.
• Spreading damage. Untreated mold can spread to neighboring rooms and upper floors, pushing repair costs higher.

Why the usual cleaning routine falls short

• Mopping with ordinary floor cleaner. It lifts stains but does not disinfect grout lines, under beds, behind wardrobes or along walls where water stood.
• Pouring strong bleach. Leaves a sharp smell tenants dislike, blotches wooden doors and furniture, and can irritate the airways.
• Painting over damp walls. The room looks new for a few weeks, then the paint blisters and peels and the mold returns.
• Charcoal bags or odor blocks. Help a little in a small room, but cannot cope with smells embedded in walls and furniture.
• Leaving it to tenants. Most tenants have neither the equipment nor the know-how, and they often feel the landlord does not care.

Landlords need a method that can be applied to many rooms quickly, works on germs, mold and odor together, and lets them tell tenants with confidence that their room has been professionally disinfected.

Why rental buildings in Don Mueang need serious recovery

Don Mueang has a large concentration of rooms for rent, apartments and dormitories, thanks to its location near the airport, universities, industrial areas and rail lines. Tenants include shift workers, students and families who want affordable housing close to work. The rental market here is competitive. Tenants have plenty of choice, and if a room has problems, moving somewhere else is easy.

Many buildings stand in narrow sois on low ground close to canals and drains. When heavy rain continues for days, water easily collects on the ground floor. Ground-floor rooms, often the cheapest in the building, are hit hardest, and they are frequently rented by families with small children or older relatives who prefer not to climb stairs. These are precisely the people most vulnerable to mold and floodwater germs.

Older buildings add further challenges: plywood built-in furniture that swells when wet, plastered walls that hold moisture, shared plumbing where sewage can back up, and limited ventilation in internal corridors. Each of these needs attention if rooms are to be truly ready.

A floor-by-floor recovery plan (example)

• Step 1: common areas first, including lobby, stairs, laundry room and parking, because every tenant walks through them.
• Step 2: ground-floor rooms that were flooded directly, one by one as each is ready.
• Step 3: upper-floor rooms with damp problems or roof leaks.
• Step 4: re-check and mosquito fogging around the building.

Following this order helps tenants who are still living in the building feel safe from day one, and lets ground-floor tenants move back gradually without waiting for the entire building to be finished.

The WHD solution: Chemgene HLD4H fogging and ozone treatment for apartments and dormitories

World Health Disinfection provides disinfection fogging and ozone treatment for rental residential buildings, planned room by room or floor by floor so tenants can return as soon as possible.

Fine-mist fogging with CHEMGENE HLD4H in rooms and common areas

The team uses CHEMGENE HLD4H applied with a ULV fogger as a fine mist that reaches under beds, behind wardrobes, into bathrooms and onto balconies, as well as corridors, stairwells, the shared laundry and parking areas. It helps reduce bacteria, viruses and mold on surfaces without the harsh smell of chlorine.

Ozone treatment to remove mold and musty odors in rooms

After fogging, each room is sealed and an ozone generator is run. Ozone gas penetrates walls, wooden wardrobes, curtains, mattresses and air-conditioning units. It helps destroy mold spores and breaks down musty, drain-like and muddy odors, then naturally reverts to oxygen.

Why both steps matter in a rental room

Rental rooms are small and full of soft and porous materials: a mattress, curtains, a plywood wardrobe, sometimes a sofa. Fogging disinfects the surfaces tenants touch every day, from the door handle and light switches to the bathroom tap and kitchen counter. Ozone reaches the places a mist cannot fully penetrate, such as mattress foam, the inside of the wardrobe and the air-conditioner, and deals with the smell that tenants notice the moment they open the door. Together they address both the hygiene and the comfort of the room.

How the work is done

1. Building survey. Flooded rooms, common areas, plumbing and areas with heavy mold are inspected.
2. Room preparation advice. For example, clearing mud, removing damaged items, checking electrics and informing tenants about their belongings.
3. Fogging of all rooms and common areas. Starting with spaces tenants share.
4. Room-by-room ozone treatment. Matched to room size and odor level.
5. Ventilation. Doors and windows are opened until no ozone smell remains.
6. Re-check. Results are reviewed and advice is given on ongoing humidity control.

10 reasons Don Mueang landlords choose WHD

1. Many rooms in one day with our fine-mist disinfection service.
2. Odors removed at the source through our ozone treatment service.
3. Common areas covered. Lobby, stairs, corridors, laundry room, parking.
4. No harsh smell for tenants to complain about. CHEMGENE HLD4H is not chlorine.
5. Helps keep existing tenants once they are confident their room is safe.
6. Lower health risk for children and older tenants on the ground floor.
7. Stops mold spreading to other rooms, reducing long-term repair costs.
8. A clear message for new tenants that the building has been disinfected.
9. Learn more about ozone in homes: residential ozone disinfection.
10. Mosquito control around the building with our mosquito fogging service.

Before and after restoring rental rooms

A landlord's perspective (illustrative scenario)

"At first I was terrified all the ground-floor tenants would leave. After the team fogged the whole building and ozone-treated the ground-floor rooms, I posted photos in our tenants' LINE group explaining what had been done. The family from Room 104 came to look, said the smell was gone, and decided to stay. I was so relieved."
— Apartment owner, Don Mueang

For small landlords, every tenant who stays is income protected and one less room to advertise. Showing tenants a clear, professional recovery process is often what makes them choose to stay.

It also changes the conversation with prospective tenants. When people message to ask about vacant rooms, a landlord who can say "the building was professionally disinfected and ozone-treated after the flood, and here are the photos" stands out from neighbors who avoid the subject. In a district where flooding is a known concern, that kind of openness is a genuine competitive advantage.

Checklist for landlords before tenants move back

• Inspect electrics in every ground-floor room. Sockets, switches and water heaters must be checked by an electrician before power is restored.
• Check water and drainage. Clean water tanks and check septic tanks and drains for backflow.
• Replace badly damaged items. Mattresses soaked for a long time and plywood wardrobes that have swollen out of shape.
• Service air-conditioners in every room affected by flooding or high humidity.
• Clean shared facilities. Laundry room, coin-operated washing machines, drinking water dispensers and parking.
• Empty standing water around the building to cut mosquito breeding.
• Communicate openly with tenants. Explain what has been done and when they can move back.
• Take before-and-after photos for deposit discussions and insurance claims.

For health guidance after floods, see Thailand's Department of Disease Control and the World Health Organization.

Communicating with tenants to keep their trust

After a flood, what tenants want most is not a long apology but clear information: when they can move back, and how safe their room will be. Landlords can do this simply.

• Use a LINE group or regular messages to share progress: when mud removal is finished, when fogging and ozone treatment take place, and when rooms are ready.
• Share photos. Pictures of rooms before and after cleaning, and of the team at work, show tenants that real care is being taken.
• Invite tenants to view their room before moving back so they can confirm for themselves that the smell has gone.
• Discuss rent fairly for the period when rooms could not be used. A reasonable approach protects the long-term relationship.

When tenants feel the landlord cares, they usually stay and speak well of the building, which is worth far more than the cost of recovery. In a competitive rental market like Don Mueang, reputation is one of the most valuable assets a landlord has.

Deposits, insurance and fair dealing after a flood

Floods raise awkward questions between landlords and tenants. Who pays for a tenant's damaged belongings? Should rent be charged for the weeks a room was unusable? What happens to the deposit if a tenant decides to leave? There is no single answer for every building, but a few principles help.

• Separate building damage from personal belongings. The landlord is normally responsible for the structure, fixtures and furniture provided with the room; tenants are usually responsible for their own possessions, often through their own insurance.
• Document everything. Dated photos of every room before and after recovery protect both sides and support insurance claims.
• Be generous where it is cheap to be generous. A short rent holiday or flexible move-back date costs little compared with a vacant room for several months.
• Put agreements in writing. A short message confirming any rent adjustment or deposit decision avoids misunderstandings later.

Professional disinfection and ozone treatment also play a role here. When a landlord can show that rooms have been properly restored, discussions about deposits and rent become calmer, because tenants can see that the problem has been taken seriously.

Preparing a flooded rental room: a practical guide for caretakers

Caretakers and cleaners do much of the hard work in small apartment buildings. A clear routine for each flooded room makes treatment day faster and the result better.

• Entrance and floor: remove all mud, including from door tracks and the gap under the door; rinse with clean water and squeegee dry.
• Bathroom: flush the floor drain and toilet, clean around the base of the toilet and under the basin, and check whether sewage has backed up from shared pipes.
• Wardrobe and cabinets: empty them, take note of swollen plywood panels for replacement, and leave doors open so mist and ozone can reach inside.
• Bed and mattress: stand mattresses on their side to air, and set aside any that were soaked in floodwater for assessment or replacement.
• Curtains: take them down and wash them; rehang only after the room has been treated.
• Air-conditioner and fridge: unplug, clean filters and drip trays, and empty and wash any fridge provided with the room.
• Electrics: keep the room's breaker off until an electrician has checked sockets and the water heater.

A simple checklist taped to each door, ticked off as each step is completed, helps the owner see at a glance which rooms are ready for the WHD team and which still need work.

Reducing the impact of the next flood

Many buildings in low-lying sois will face heavy rain again. A few practical changes can make the next recovery faster and cheaper.

• Raise what you can. Mount electrical sockets and water heaters higher on ground-floor walls, and choose wardrobes on legs rather than plywood units that sit on the floor.
• Choose water-tolerant finishes. Tiles, cement-based plaster and moisture-resistant paint recover far better than wallpaper and particleboard.
• Prepare a tenant plan. Keep an up-to-date contact list, agree in advance where tenants can store belongings upstairs, and tell them how you will communicate during a flood.
• Keep drains clear. Clean gutters and drains before the rainy season and check for blockages that make flooding worse.
• Know your recovery partners. Save the numbers of an electrician, a plumber and a disinfection provider so that you can book quickly when the water goes down.

Landlords who plan ahead usually reopen rooms days or even weeks earlier than those who start from scratch each time.

Frequently asked questions

Do tenants need to remove their belongings first?
Damaged items should be taken out of flooded rooms. Usable belongings can stay during fogging. For ozone treatment, the team will advise how to handle valuables, food and plants.

Do tenants on upper floors need to leave the building?
Usually not. The team seals only the rooms being ozone-treated and notifies neighboring tenants in advance.

How many rooms can be done in a day?
It depends on room size and damage. The team will assess and plan so tenants can move back as quickly as possible.

Do freshly painted rooms still need ozone treatment?
If the wall behind the paint is still damp or there is still a smell, ozone treatment helps reduce mold and odor, and also helps with new-paint smells. See ozone odor and chemical residue removal.

Do you also remove dust mites from mattresses?
Yes. For furnished rooms, our dust-mite removal service can be combined with the treatment.

How can we look after rooms between tenancies ourselves?
Use the CHEMGENE 750 ml spray on touch points, and consider a Master Ozone Generator to treat rooms before new tenants move in.

Do you serve buildings outside Don Mueang?
Yes. WHD works across Bangkok, the surrounding provinces and other areas. Call to check coverage and arrange a survey.

Welcome your tenants home with confidence

Talk to the World Health Disinfection team about restoring your apartment, dormitory or rental rooms after the flood.

See Disinfection Service – Click Here

Book Ozone Treatment – Click Here

Call 065-556-6294 · LINE @whd268 · Email worldhealthdisinfection@gmail.com

Related links

• Residential ozone disinfection
• Dust-mite removal service
• Mosquito fogging service
• All articles
• External source: WHO – Floods and health

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