The UK method, adapted for tropical water systems
The process of a risk assessment is the same anywhere: survey the systems, find where bacteria can grow and reach people, score the risk, set controls and a monitoring routine, name who is responsible. What changes in Thailand is the physics, and therefore the numbers. We adapt the controls; we do not lower the bar.
Four things that are different here
Chlorine residual is the main cold-water control
In the UK the cold system is kept below 20 °C and the mains residual is taken for granted. In Thailand cold water cannot be held below 20 °C, so the residual of free chlorine, from the incoming supply to the furthest tap, is the control that matters. We measure it at the supply, the tank outlets and sentinel outlets, with pH, because the failures Thai investigators keep finding are specific: dosing points left in the sun, auto-chlorinators broken for months, tablets dropped in without measuring, and municipal supplies arriving with none.
Tanks, turnover and three water sources
Almost every building stores water underground and on the roof, fed by the municipal supply, tanker deliveries, a borehole, or all three. Our schematics show every tank, inlet and dosing point, and the assessment looks at capacity against low-season demand, sediment, covers and where chlorine is added relative to storage.
Hot water run at 40 to 50 °C by design
Heat pumps are the norm and operators set them low to save energy. In Thai case investigations from 2013 to 2024, 85.71% of accommodations had hot water below 50 °C or free chlorine below the cited level, and showers and taps, not cooling towers, are the commonest positive points. We check storage setpoints, return-loop temperatures and the furthest rooms, and we make the energy case for 60 °C storage with the numbers.
Low-season closure and reopening
Wings, floors, spas and towers are shut for months and brought back for high season. The written scheme includes a mothballing and recommissioning procedure for each, which is also what tour operators ask for before guests return.
The numbers, side by side
Thai guidance, the UK method and the European benchmark are not far apart on controls. They differ most on what counts as a problem result.
| Parameter | Thai Department of Health guidance | UK HSG274 | European 15-point plan / ECDC |
|---|---|---|---|
| Hot water stored | Above 60 °C generated; storage at least 42 °C | At least 60 °C | 50 to 60 °C throughout the system |
| Hot water at the tap | Above 50 °C at every outlet | At least 50 °C within one minute | 50 to 60 °C |
| Cold water | Not specified in the guideline table | Below 20 °C within two minutes | Below 20 °C at all outlets |
| Free chlorine | At least 0.2 mg/L in tanks, checked daily; 0.2 to 0.5 mg/L in rooms | Not a routine control; temperature instead | Spa pools 2 to 3 mg/L |
| Legionella sampling | Every six months to the Department of Medical Sciences | Cooling towers quarterly; domestic water where control is in doubt | Not prescribed |
| Action level, hot and cold water | Under 100,000 CFU/L "may not be satisfactory"; 100,000 to 1,000,000 "potential hazard"; above 1,000,000 shut down | Above 100 cfu/L review; above 1,000 cfu/L disinfect and resample | 1,000 cfu/L benchmark |
| Cooling towers | Cleaned one to two times a month; 10 mg/L shock for three to six hours | Twice a year clean; above 10,000 cfu/L immediate action | Cleaned and disinfected at least twice a year |
| Written plan | Water management plan and records; a responsible officer | Risk assessment and written scheme, reviewed regularly | A documented 15-point plan and a trained responsible person |
Thai action levels are a hundred times higher than the UK's. A result of 5,000 CFU/L sits in the lowest band of the Thai table, where the response is to revise the maintenance plan, and is a disinfect-and-resample result in the UK. Our schemes set the limits at the European level because that is the level investigators and claimant solicitors compare against, and we say so in the report. The Department of Health's 2026 study proposed new national bands and a central reporting database; we will update the scheme when they are issued.
Why sampling alone is not control
A sample is a snapshot of one tap on one day, read a week later. Thai Department of Health criteria for hotels come down to three checks: the laboratory says "not detected", free chlorine is at least 0.2 mg/L, hot water is at least 50 °C. Hotels that meet those three on the day of the test still fail between tests, because nothing tells them when the dosing stopped or the heater drifted. A written scheme does: it sets the limits, the checks, the person and the record, so the six-monthly sample becomes confirmation rather than discovery.
The clearest case is the one Thai investigators wrote up themselves. A certified Phuket hotel with two contractors testing regularly and clean results was found with heavily contaminated cooling towers after three European guests fell ill in early 2025. The investigators recommended that samples be taken by someone other than the maintenance contractor and verified against the laboratory's original certificates. That is the role we fill.
Sources:Bureau of Environmental Health guideline;Department of Disease Control;Niakul 2025;Pensuk et al. 2026;Division of Epidemiology 2025;Tangkuha et al. 2026;WESR 2023;HSE HSG274;ECDC Form B;TUI 15-point plan.
Get a quote for your property
Tell us the property type, where it is, how many rooms and whether it has cooling towers. We reply with a price and the earliest survey date, usually the same working day.
Had a positive result, or a notification about a guest?
What you do and record in the first 24 hours is what investigators and tour operators will read later. Get in touch now for advice on disinfection, independent resampling and the evidence they will ask for.