A Story from the Field: A 1 a.m. Email from a Tenant Who Has Just Flown Home

Wanna owns a one-bedroom unit in a small, low-rise condominium building on a quiet soi off Sukhumvit in Watthana. For almost two years she has rented it on a long-term lease to Daniel, a European engineer working for a multinational company. The unit is on the ground floor, with a small terrace opening onto the building's garden. It is the feature Daniel liked most when he first viewed the place.

During the days of heavy rain and flooding in the soi, Daniel happened to be overseas on a work trip. Water from the street flowed into the car park and onto the ground-floor terraces, then seeped into the unit. It was only a few centimetres deep, but it stood for almost two days before it drained away. Nobody went in to open the windows, because the tenant was not there.

Ten days later, at one o'clock in the morning, Wanna received an email. Daniel wrote that he had opened the door to a powerful musty smell. The rug under the sofa was damp. There were black mold spots on the back panel of the built-in wardrobe. The suits hanging inside smelled sour, and he had checked into a hotel for the night. The last line of the email kept Wanna awake until dawn: he asked for a plan to fix the problem within two days, and said he was now considering whether to renew the lease.

For landlords who rent to international tenants, a reliable tenant who pays on time and looks after the unit is hard to find. Losing one can mean months of vacancy, another agent's commission, and the risk that the unit's reputation is discussed among relocation agents, HR departments and expat community groups. This article walks through how to respond, from the very first email to restoring the unit so that it is genuinely pleasant to live in again.

Why a Few Centimetres of Water Can Leave a Condo Smelling So Bad

Landlords are often surprised that such a shallow flood can create such a strong smell. The reason is a combination of time, closed spaces and absorbent materials.

• The unit was sealed while the tenant was away. With no one opening windows or running the air conditioning, humidity inside builds up quickly. Mold usually begins to grow within 24 to 48 hours of a material getting wet, and by day ten it can be well established.
• Rugs and fabrics soak up water. Area rugs, curtains, upholstered sofas and mattresses hold moisture and odour deep in their fibres, even when the surface looks and feels dry.
• Built-in furniture is usually made of engineered board. When the bottom edge of particleboard or MDF gets wet, it swells and traps moisture against the wall behind the cabinet, a hidden spot where mold grows easily.
• Drains and terrace gullies may carry street water. Floodwater can push mud and debris into the drainage system, so sewer-like smells may rise from the bathroom floor drain or the terrace outlet.
• The air conditioner recirculates spores. When the tenant switches the air conditioning back on, air carrying spores is spread throughout the room, and a damp indoor coil can become a source of odour in its own right.

The Full Impact Landlords Need to Consider

The tenant's health. Floodwater from the street can carry bacteria such as E. coli and the bacteria that cause leptospirosis. Mold spores can trigger allergies, asthma, a blocked nose and itchy eyes. Some tenants who come from drier climates find tropical mold more irritating than they expected, and a tenant who feels unwell at home is unlikely to stay long.

Rental income. A tenant may ask for a rent reduction for the days the unit cannot be used, for help with temporary accommodation, or may decide not to renew. What applies depends on the lease and on what the two parties agree.

Reputation. Many international tenants find homes through relocation companies or their employer's HR team, and they share experiences in online groups. A fast, professional response protects your ability to rent the unit in future, while a slow or defensive one can follow the property for years.

How to Respond to the Tenant in the First 48 Hours

1. Reply quickly, acknowledge the problem and do not argue. Thank the tenant for letting you know, show genuine concern for their health, and give a specific date for an inspection.
2. Arrange a joint inspection. Always ask permission before entering the unit. Take photos and video of the condition of the room, the mold spots, the water line and any damaged items.
3. Separate your property from the tenant's. Furniture supplied with the unit is something the owner needs to deal with. Clothing, documents and personal belongings belong to the tenant, and the tenant should decide how they want them handled.
4. Talk to the building's juristic person. Ask how the water got in, whether the building's drainage had a problem, and whether the management plans to disinfect the common areas.
5. Present a plan with dates. For example: the day the rug and sofa are removed, the day of disinfection and ozone treatment, the ventilation period, and the day you will walk through the unit together.
6. Discuss rent or temporary accommodation openly. Refer to the lease and put any agreement in writing. If you are unsure about the legal position, ask your agent or a legal adviser.

Most tenants do not expect a landlord to stop a flood. What they do expect is that the landlord takes responsibility, communicates clearly and fixes the problem properly. A plan with clear steps and real dates is often what turns frustration back into trust.

Fixes Landlords Often Try That Do Not Work

• Sending a maid to wipe everything with bleach. This can remove some stains from hard surfaces, but it does nothing about mold inside the rug, behind the wardrobe or in the air. A strong chlorine smell in a closed room may also annoy the tenant even more than the original problem.
• Charcoal bags and scented diffusers. They reduce the smell slightly or hide it for a while, but a tenant who lives there every day will notice at once that the musty smell is still there underneath.
• One dehumidifier for the whole unit. It helps, but if the rug and the back of the wardrobe are still damp and already moldy, a dehumidifier alone does not kill anything.
• Painting over mold on the walls. The mold will push the paint into blisters before long, and a tenant who notices will feel the problem was covered up rather than solved.
• Waiting to see if the smell fades. In a ground-floor unit in Bangkok's humid season, it rarely does. Time usually makes it worse.

The Professional Solution: Ozone Treatment Plus Chemgene HLD4H Disinfection Fogging

World Health Disinfection (WHD) provides ozone treatment and disinfection fogging for condominium units after flooding. We schedule the work around the tenant's availability and the building's rules for contractors.

How the Work Is Done

1. Survey with the owner or tenant. We look behind the wardrobe, under rugs, along door frames, in the bathroom and on the terrace, and assess which materials should be removed or replaced.
2. Preparation advice. Waterlogged rugs, fabrics and upholstered furniture are taken out for cleaning or disposal as appropriate. The tenant removes or covers valuables, documents and delicate electronics. If the air conditioner smells, an air-conditioning technician should clean the indoor coil.
3. Disinfection fogging with Chemgene HLD4H. We use CHEMGENE HLD4H through an ultra-low-volume fogger, so the fine mist reaches behind cabinets, under the bed, into door gaps and around the bathroom.
4. Ozone shock treatment. A Master Ozone Generator runs in the sealed unit, helping to destroy airborne mold spores and break down the odour molecules trapped in curtains, mattresses and cabinets.
5. Ventilation. Windows and the terrace door are opened until the ozone has broken down, before the tenant returns.
6. Re-check and aftercare advice. We assess the smell together with the tenant where possible and give practical advice on humidity control for a ground-floor unit.

10 Reasons Rental Owners Choose Ozone Treatment and Disinfection After a Flood

1. It shows the tenant you are serious. Bringing in a professional team with a clear plan says more about responsibility than any apology.
2. It removes musty odour at the source. Ozone treatment breaks odour molecules down rather than masking them.
3. It reduces germs on surfaces the tenant touches every day. Disinfection fogging covers floors, walls, the bathroom and the terrace.
4. It reduces airborne mold spores. Tenants with allergies feel the difference.
5. It is quick. Most jobs are completed within a day, which keeps the number of nights the tenant spends elsewhere to a minimum.
6. It reaches places a cleaner cannot. Behind built-in wardrobes, under beds and in the gaps around bathroom fittings.
7. It protects the long-term value of the unit. A unit without a musty smell is far easier to re-let.
8. It uses a purpose-made disinfectant. CHEMGENE HLD4H is what our team uses for fogging.
9. It works within building rules. Our team follows the access procedures and working hours set by the juristic person.
10. It can be combined with mattress and sofa care. Add our dust mite removal service for mattresses and sofas that were not submerged but absorbed humidity.

A Sample Reply to Your Tenant (Adapt as Needed)

Many owners are unsure how to word their reply, especially in a second language. A short, polite message with clear dates goes a long way. Here is a template you can adapt:

A message like this tells the tenant three things: you understand the problem, you have a plan, and you have dates. That is usually enough to lower the temperature of the conversation.

Preventing a Repeat in a Ground-Floor Unit

Ground-floor units with terraces are lovely to live in, but they are the first to feel the effects of heavy rain. A few simple measures reduce the risk next time.

• Agree with the tenant on what to do before long trips during the rainy season, such as lifting rugs, leaving wardrobe doors ajar and setting a dehumidifier.
• Ask the juristic person whether the terrace drains and the soi drainage are cleared before the monsoon.
• Consider a simple threshold or flood board for the terrace door if water has entered more than once.
• Choose washable or moisture-resistant rugs and furniture for the ground floor.
• Have the air conditioner cleaned on a regular schedule, and ask the tenant to report any musty smell from the vents early.
• Keep a short, bilingual contact sheet in the unit with your number, the building office and a trusted service team.

Small steps like these show the tenant that you are thinking ahead, which matters a great deal to long-term renters choosing whether to stay.

What the Inspection Should Cover, Room by Room

A joint inspection is more useful when both sides know what they are looking for. Walking through the unit in a fixed order also helps you produce a clear record that the tenant, the agent and the building office can all understand.

• Entrance and living room: check the floor along the door threshold, the skirting boards, the underside of the sofa and any rug. Lift the rug to look at the floor beneath it, and note whether the smell is stronger near the floor than at head height.
• Bedroom: open the wardrobe and look at the back panel, the bottom shelf and the base of the doors. Check the underside of the bed frame and the bottom edge of the mattress. Smell the curtains near the hem, where they may have touched water.
• Kitchen: look inside the cabinet under the sink, behind the refrigerator and under the bottom drawer. These are classic hiding places for mold after a ground-floor flood.
• Bathroom: run water into the floor drain and the basin, and notice whether a sewer smell rises. Look at the silicone around the shower and the base of the door frame.
• Terrace: check the drainage outlet for mud, look at the door sill and any outdoor furniture cushions, and see whether water marks run up the outside wall.
• Air conditioning: switch the unit on for a few minutes and smell the air from the vents. A sour smell usually means the coil and drain tray need a professional clean.

Write a simple list of what you found, add photos, and share it with the tenant the same day. The list then becomes the checklist for the final walk-through after treatment.

Working with the Building Office and the Relocation Agent

For many expat leases, the landlord is not the only party involved. The building's juristic person controls access, working hours and common areas, and a relocation agent or the tenant's employer may be following the case closely. Keeping everyone informed avoids delays and misunderstandings.

Let the building office know the date and time of the treatment in advance, together with the names of the service team, and ask whether the lift or service entrance needs to be booked. If the building is planning to disinfect the car park, lobby or corridors, try to schedule your unit on a nearby day so the improvement is consistent from the front door to the bedroom.

If the tenant came through a relocation agent, a short update to the agent showing the plan and the dates is often appreciated. It reassures the agent that the issue is being handled responsibly, which matters when they recommend properties to future clients.

An Owner's Perspective

"When that first email arrived, I was really stressed. I was sure he would move out. I replied with a plan and clear dates, had the rug taken out, and booked the disinfection and ozone treatment. He calmed down a lot. On the day he moved back in he said the room smelled completely different from the first day, and he decided to stay."
— Wanna (name changed), condo owner on Sukhumvit, Watthana

This is an illustrative scenario based on situations commonly seen after floods. Actual results depend on the condition of each unit.

Frequently Asked Questions

Q: The tenant is still living in the unit. How can ozone treatment be done?
A: We schedule a day when the tenant can be out. Nobody, including pets, may be inside during treatment, and plants should be removed. After treatment the unit must be ventilated before anyone returns. Our team will advise on suitable timing.

Q: What about the tenant's clothes and belongings?
A: The tenant should decide whether to send items for cleaning, store them separately or take them out beforehand. We usually recommend that clothes that have absorbed the smell are laundered or dry-cleaned, and that delicate electronics are covered or removed.

Q: Should a flooded rug be cleaned or thrown away?
A: A rug that sat in street floodwater for hours and already smells or shows mold is usually best replaced. A small rug that was only briefly wet may be suitable for professional cleaning, depending on its condition.

Q: Who should pay for the service?
A: In general, the owner is responsible for the condition of the unit and the furniture supplied with it, but the details depend on the lease and on what the parties agree.

Q: Does the building management need to approve the work?
A: Most condominiums have rules about contractors entering the building. Notify the juristic person in advance. The WHD team can provide names and working times as the building requires.

Q: Is one treatment enough?
A: If waterlogged materials are removed and humidity is controlled, one treatment usually makes a clear difference. Ground-floor units that still have rising damp may need monitoring and, in some cases, a follow-up treatment.

Q: Can the tenant's work laptop and monitors stay in the room?
A: It is better to take personal laptops and sensitive equipment out for the day. Larger items such as a television can be covered, and our team keeps the ozone dose controlled.

Give Your Tenant a Home They Can Breathe In Again

WHD serves condominiums across Sukhumvit, Thonglor, Ekkamai, Phrom Phong and the wider Watthana district.

Book Ozone Treatment – Click Here

View Disinfection Service – Click Here

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

Related Links

• Residential ozone disinfection
• Ozone treatment for odours and chemical residue
• Dust mite removal service
• All articles

Health reference: World Health Organization (WHO): Floods · Department of Disease Control, Thailand