What happened in Bangkok in late September 2026

According to news reports, between 24 and 27 September 2026 Bangkok received roughly 300 mm of rain in about 48 hours. Streets, homes and community buildings flooded across the city, and on 26 September the Bangkok Metropolitan Administration declared all 50 districts a disaster zone. Eastern Bangkok was hit hardest, with areas such as Khlong Chan and Bueng Kum mentioned in coverage. Governor Chadchart said the canals were full and that drainage would take two to three days after the rain stopped.

Reports also noted three deaths, and we extend our sincere condolences to the families who lost loved ones. As of 30 September, some roads, including Si Burapha and Lat Phrao, still had 20 to 40 cm of standing water. Thai media compared the event with the great flood of 2011, and one Thai business report cited a Chamber of Commerce estimate of about 12,300 million baht in damage.

In every flood, community places of worship quietly become the first line of support. Mosques, small neighbourhood surau, Buddhist temples, churches and shrines turn into food kitchens, collection points for relief bags and temporary shelters. When the water finally drains, these same buildings face the same problems as everyone's homes: dampness, germs and mold hidden in carpets, curtains and walls. This guide explains how mosque committees and caretakers of other places of worship can restore their buildings in the right order, and where professional ozone disinfection fits into that process.

A typical scenario (an illustrative situation based on common post-flood experiences, not a review from a specific customer)

The first Friday after the water went down

Arif serves on the committee of a small community mosque near a canal in eastern Bangkok. The single-storey building was paid for by local families over a generation. At the front is a prayer hall covered wall to wall in dark green carpet. Along one side runs a row of ablution taps. At the back is a classroom where neighbourhood children come every Saturday and Sunday afternoon for religious lessons.

When the rain kept falling, canal water crept across the courtyard first, then slowly into the prayer hall until it was nearly knee deep. Even then, the mosque did its job. The mezzanine became a store for relief bags. A temporary kitchen on the veranda cooked meals for the neighbourhood. Volunteers waded in and out dozens of times a day.

Three days after the floor finally dried, Arif and the volunteers dragged the big carpets into the sun, scrubbed the floor, rinsed out the ablution area and left every fan running overnight. Yet on the Friday morning when everyone hoped to pray together again for the first time, a heavy, damp smell still filled the hall. Small black dots had appeared in a line along the canal-side wall. The curtain that separates the women's section carried a yellow tide mark. One elderly man with asthma had to step outside because he could not stop coughing.

The committee's question afterwards was simple: "We washed it and we dried it. Why does it still smell, and how can we be sure the children can come back safely?" Answering that question starts with understanding what floodwater leaves behind in a place of worship.

What floodwater leaves behind in a mosque

Bangkok floodwater is not clean rainwater. It mixes with canal water, overflowing drains and, in places, sewage from septic tanks and wastewater pipes. Public health agencies, including the US CDC and Thailand's Department of Disease Control, warn that floodwater can carry faecal bacteria, viruses that cause diarrhoea, and leptospirosis bacteria from rodent urine. When the water recedes, these germs do not leave with it. They remain in mud, silt films and any material that soaked up the water.

Risk points that are unique to places of worship

Prayer carpets and mats. Most mosques lay large carpets across the entire hall. Carpets have a pile layer and a backing that hold a great deal of water. If they are not fully dried within a day or two, the underside becomes a mold nursery that nobody sees from above. Just as important, worshippers prostrate several times a day with forehead and nose touching the carpet, which puts their faces closer to spores and dust than almost any other everyday activity.

Ablution areas. These areas are wet every day even in normal times. After a flood, floor drains can clog with silt, and tile grout, benches and shoe racks collect biofilm. People wash their faces, rinse their mouths and clean their noses here, so this is a space that needs to be especially clean.

Classrooms and libraries. Children's classrooms often have low tables, floor cushions, bookshelves and document cabinets. Paper and cloth book covers absorb moisture easily. Stored in a damp room after the flood, books can develop mold spots along their edges surprisingly quickly, which is both a health concern and a painful loss of items with deep spiritual value.

Community kitchens. Many places of worship have a kitchen for religious festivals, weddings, funerals and breaking-fast meals. During the flood these kitchens may be used far more intensively than usual. Pots, trays, utensils and floors all need thorough washing and sanitising before normal use resumes.

Curtains, partitions and ceiling fans. Long curtains used as partitions or sun screens often touch the floor and wick water up through their fibres. Ceiling fans and air conditioners running in a damp room can circulate spores throughout the space.

Mold and musty air: slow to arrive, slow to leave

The WHO and CDC both advise cleaning and drying buildings within 24 to 48 hours after floodwater recedes to limit mold growth. In reality, most places of worship were still serving as relief centres during that window and simply could not clean in time. Mold growing on plaster, wood and carpet releases spores and the compounds that create the familiar musty smell. These can trigger allergies, sneezing, blocked noses, eye irritation and asthma flare-ups.

Who is most at risk in a faith community

• Older adults, who often attend prayers and activities most regularly and frequently live with chronic conditions.
• Children in religious classes, who sit on the floor, play on carpets and touch their mouths without thinking.
• Pregnant women, whose immune systems change during pregnancy.
• People with chronic illness such as diabetes, lung or heart disease, or weakened immunity.
• Volunteers who waded through floodwater. Anyone with a high fever, headache, calf pain after wading, diarrhoea or an infected wound should see a doctor promptly, as these can be signs of leptospirosis or other infections.

The real cost of leaving dampness and germs behind

Community health. A place of worship gathers many people in one room at the same time, whether for Friday prayers, festivals, communal meals or classes. If the air carries mold spores or surfaces still harbour germs, the risk is not limited to one person. It spreads across many households at once.

Donated money. Most community places of worship survive on donations. Every large carpet, curtain, bookcase and air conditioner represents money that local families saved and gave. If mold spreads until everything has to be thrown away or walls have to be rebuilt, the cost will be many times higher than handling the problem properly from the start.

Time and religious life. Every day the prayer hall stays closed, worshippers must travel elsewhere or pray separately at home. Children's lessons are postponed. Booked weddings and gatherings are cancelled. The rhythm of community life stops.

Trust. Parents will not send children back while they can still smell damp or see mold on the walls. Older people with health conditions may decide to stay away.

Why the usual quick fixes fall short

Pouring bleach across the floor. Correctly diluted bleach can sanitise hard surfaces after dirt is removed, but it cannot be used on carpets or fabric without fading and damaging them. It does nothing for the air in the room, and mixing it with other cleaners can release dangerous gases. A sharp chlorine smell is also a poor fit for a hall where people put their faces to the floor.

Running every fan at full speed. Fans do help remove moisture. But in a room where mold has already started, strong airflow lifts spores and spreads them into other carpets and curtains.

Burning incense or spraying air freshener. Fragrance covers a musty smell for a while but does not reduce germs or spores.

Painting over mold stains. This is a very common shortcut in public buildings because it makes walls look clean before an important event. If the wall is still damp inside and the mold's roots remain, the stains return within weeks and the smell never really leaves.

Sunning carpets for a single day. Sunlight helps the top, but the backing and underlay often stay damp. Laid back down on a concrete floor that has not dried, the carpet becomes a hidden place for mold to grow.

The shared limit of all these methods is that they only reach what hands can touch and eyes can see. Germs and spores are also in the air, in corners, under shelves, inside air-conditioner vents and on hundreds of touch points no one will ever wipe. That gap is exactly where ozone disinfection helps.

How ozone disinfection works for mosques and places of worship

Ozone (O₃) is oxygen with one extra atom. It is a strong oxidiser. Released into a closed room at a controlled concentration, it spreads through the entire space, including corners that cloths and sprays never reach, and breaks down the cell structures of viruses, bacteria and mold as well as the molecules that cause musty odours. It then reverts to ordinary oxygen (O₂), leaving no chemical residue on carpets, curtains, books or the floor where people prostrate.

According to the test results certified for the company, World Health Disinfection's service has been tested by Thailand's Department of Medical Sciences and by Intertek in the UK, eliminating viruses, bacteria and mold by 99.99%. You can review the details on the certificates page.

Two rules that come first

Rule one: the space must be empty. Ozone at disinfecting concentrations is harmful to the lungs. Every room being treated must be closed with no people, pets or plants inside, and everyone stays out until the technicians confirm that the rest and ventilation period is over. For a place of worship, this means planning the schedule around prayer times, ceremonies and classes.

Rule two: clean and dry first. Ozone does not replace mud removal, floor washing, scrubbing stains or drying carpets. It is the step after the space is clean and reasonably dry, used to deal with remaining germs in the air and on surfaces and to reduce stubborn musty smells. If a carpet soaked in sewage-contaminated water for a long time and cannot be cleaned and dried, removing it remains the safer choice.

The zone-by-zone process

1. Survey and plan with the committee. Technicians assess the prayer hall, ablution area, classrooms, storerooms and kitchen, and ask about the religious schedule so treatment happens only when the building is genuinely empty.
2. Divide the building into zones, for example the men's hall, the women's hall, the ablution area, the classroom and the kitchen, so each receives the right concentration.
3. Prepare the space. Close doors and windows, switch off fans and air conditioning as advised, open cupboards and drawers so the gas can reach inside, and move out any items the team recommends.
4. Ozone release and contact time. The generator runs in the sealed room. A typical cycle is about 30 minutes per zone, depending on size and site conditions.
5. Rest and ventilate. The ozone is allowed to break down into oxygen, then doors and windows are opened. No one goes in until the technicians say it is safe.
6. Handover, with advice on ongoing moisture control so mold does not come back.

For ozone jobs of 15,000 baht or more, you also receive a free medical-grade disinfectant spray, which is useful for wiping frequent touch points after handover, such as door handles, ablution taps and handrails. See the full residential and building ozone disinfection service.

10 reasons mosque committees choose ozone as the final recovery step

1. No residue where people prostrate. Ozone reverts to oxygen, so there is no chemical film on carpets or floors that touch foreheads and palms.
2. Reaches every corner of an older building. Community buildings are full of hidden spaces behind cabinets, beneath bookshelves and around the minbar that cloths cannot reach but gas can.
3. Treats the air, not just surfaces. Spores and germs floating in a large hall are handled at the same time. Learn more on the ozone disinfection service page.
4. Tackles musty odour at its source instead of covering it with incense or perfume, so worshippers breathe more comfortably.
5. Protects donated carpets and curtains from harsh liquids that fade colours or weaken fibres.
6. Helps classrooms reopen with confidence. Parents feel reassured when the whole room has been treated.
7. Short treatment windows. About 30 minutes per zone, so work can be scheduled between prayer times or overnight.
8. Backed by testing, according to the results certified for the company by the Department of Medical Sciences and Intertek UK.
9. Experience with many building types, from homes and condos to hotels, offices, schools and hospitals, so the team understands working respectfully around how a space is used.
10. A long-term plan, not a one-off spray, including humidity advice after the flood. Ask questions or book through the WHD ozone service.

Before and after a properly ordered recovery

Example case: a three-day plan for a canal-side mosque

This example case is a hypothetical scenario used to explain the process. It is not a review or quote from a real customer.

Back at Arif's mosque, the committee agreed not to rush the children's classes back and not to paint over the walls. Instead, they would do everything in order.

Day one. Volunteers in rubber gloves, boots and masks lifted out the carpets whose backing was soaked and smelled of stagnant water. The committee decided to discard the sections that had been underwater longest and send the rest, still in good condition, for professional cleaning. All curtains came down for washing. The concrete floor was scrubbed with clean water and detergent, and every door and window stayed open all day.

Day two. A local builder checked the canal-side wall and found the lower plaster still wet, so part of the surface was opened to let moisture escape. In the classroom, books were sorted. Those soaked beyond saving were set aside respectfully, while dry ones went into temporary storage at a committee member's house. Every pot and tray in the kitchen was washed in hot water and detergent.

Day three. After the night prayer, once everyone had gone home, the ozone team arrived as scheduled and worked through five zones: the men's hall, the women's hall, the ablution area, the classroom and the kitchen. Each zone was sealed with nobody inside. After the contact time and rest period, the team opened doors and windows to ventilate, then handed the building back with advice to keep windows open during the day for several more days.

In a case like this, what the committee gains is not just a better-smelling hall but the confidence to tell neighbours the building has been restored systematically. As for the elderly man with asthma, the committee encouraged him to see a doctor rather than assume everything was fine once the smell had gone.

Recovery checklist for places of worship

Before calling an ozone team

• Check electrical safety first. If sockets or wiring were underwater, have an electrician inspect and isolate power before anyone works inside.
• Every volunteer wears rubber gloves, boots and a mask, and washes hands before eating.
• Remove mud and debris, then wash floors with clean water and detergent, focusing on ablution areas and kitchens.
• Lift carpets, mats and cushions to dry. Consider discarding carpets soaked in contaminated water that cannot be dried.
• Take down and wash all curtains and partitions.
• Sort wet books and documents, handling damaged religious texts according to your community's own guidance.
• Open doors and windows for airflow and check which walls are still damp.
• Agree with the imam or religious leaders when the building can be empty, and tell the community in advance.

On treatment day

• Confirm no people, animals or plants are inside, including anyone who may be sleeping in a back room.
• Put "do not enter" signs on every door and assign one committee member to watch the entrance.
• Open cupboards, drawers and inner doors as the technicians advise.

After treatment

• Enter only when the technicians confirm that the rest and ventilation period is over.
• Keep windows open during the day and use a dehumidifier if available.
• Wipe frequent touch points regularly, such as taps, handles, handrails and shoe racks.
• Check walls weekly for new mold spots. If they return, find the moisture source first.
• Anyone who feels unwell after wading through floodwater or after returning to the building should see a doctor promptly.

Frequently asked questions

Will ozone leave residue on the prayer carpet?

Ozone is a gas that reverts to oxygen, so it does not leave a liquid or film on carpets or floors. You must still wait until the rest and ventilation period is complete before using the space. For religious questions about the use of the hall, please consult your imam or community religious leaders directly.

Can we treat the hall while people are still coming to pray?

Not in the zone being treated. A treated zone must always be empty. The best approach is to schedule treatment when the building is free, such as late evening, or to split zones so one area can be used while another is sealed, provided the air between them is truly separated.

Should we keep a flooded carpet and ozone it, or throw it away?

If a carpet soaked in sewage or canal water for a long time and cannot be cleaned and fully dried quickly, agencies such as the CDC advise considering disposal. Ozone does not rescue a carpet whose backing is still wet with mold growing in it. It is suited to carpets that are already clean and dry, to reduce remaining germs and odour.

Do we need to move holy books and items of spiritual value?

The team will advise case by case. Wet or damaged items should be separated and dealt with first. Items of high spiritual value, or materials the community is concerned about, can be moved to a dry place temporarily during treatment.

How long does it take?

Typically about 30 minutes per zone, not including preparation, rest and ventilation. A building with several rooms can be treated zone by zone in one night or split across sessions to fit the religious schedule.

If the building has been treated, do sick people still need a doctor?

Yes. Ozone treatment improves the environment; it is not medical treatment. Anyone with fever, calf pain, diarrhoea, rashes or breathing problems, especially after wading through floodwater, should see a doctor promptly.

Does this work for temples, churches and shrines too?

Yes. The same principles apply to any indoor religious space, such as temple halls, monks' quarters, storerooms, meeting rooms and Sunday school classrooms. Simply respect the ceremonial schedule and treat only empty spaces.

Help your community's place of worship become a safe refuge again

Talk to our team about a zone-by-zone ozone disinfection plan that fits around your prayer times and activities.

Book Ozone Disinfection

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

Related services and reading

• Residential and building ozone disinfection
• Ozone removal of chemical residue and paint odours after repairs
• Chemgene HLD4H medical-grade disinfectant
• Certificates and test results
• Contact World Health Disinfection

References

• 2026 Bangkok floods – Wikipedia
• Al Jazeera: Disaster zone declared across Bangkok
• CDC – Floods and cleanup
• WHO fact sheets