Legionella Control for Cooling Towers
Updated
Legionella control in a cooling tower is a water management programme that keeps the bacteria from growing and from spreading in the tower’s drift. It combines a risk assessment, biocides with a measured residual, biodispersant, scale and corrosion control, periodic cleaning and disinfection, testing and records. PT Beta Pramesti Asia supplies the chemicals, cleaning and programme support for building and industrial cooling towers in Indonesia.
Updated: 12 November 2026.
What is Legionella and why are cooling towers a risk?
Legionella are freshwater bacteria that cause legionellosis. According to the WHO legionellosis fact sheet, the most common route of infection is inhaling aerosols from contaminated water, and cooling towers are one source of such aerosols. WHO also notes that no direct person-to-person transmission has been reported. The disease takes two forms: Legionnaires’ disease (pneumonia) and the milder Pontiac fever. WHO names immunocompromised patients as the most susceptible; risk is also higher in people over 50, smokers and people with chronic lung or kidney disease.
Cooling towers cool water by evaporation and release aerosol to the air. The CDC cooling tower guidance (updated 3 January 2025) lists four factors that favour Legionella growth: sediment and biofilm, water temperature in the 25–45 °C range, water age (stagnant or low-flow water) and inadequate disinfectant residual. Circulating water in Indonesian cooling towers can sit within that temperature range, so biofilm and disinfectant control decide the outcome.
What does a Legionella control programme contain?
A sound programme does not rely on one chemical. CDC recommends a water management programme to establish, track and improve operation and maintenance. The elements below are drawn from the CDC and WHO guidance above.
| Programme element | What is done | Records kept |
|---|---|---|
| Risk assessment | Map the tower, basin, dead legs, low-flow runs, distance to building air intakes and drift eliminator condition | System diagram, control points and written control limits |
| Oxidising biocide | Continuous or scheduled feed with a measurable residual through the day | Oxidant residual and pH log suited to the disinfectant |
| Non-oxidising biocide | Used in rotation or alongside, at the label concentration and contact time | Schedule, dose and contact-time records |
| Biodispersant | Helps loosen and disperse biofilm so biocides reach the microbes | Basin and fill condition, microbiology trend |
| Scale, corrosion and sediment control | Scale and corrosion inhibitors, automated blowdown, side-stream filtration where needed | Conductivity, inhibitor residual, corrosion rate and blowdown records |
| Cleaning and disinfection | Before commissioning, before restart after idle periods, and periodically | Cleaning reports, before-and-after photos and post-work test results |
| Monitoring and testing | Daily chemistry; scheduled microbiology and Legionella tests in a laboratory | Dated results from consistent sample points |
| Corrective actions | Tiered steps from online correction to offline emergency cleaning and disinfection | Event, action and retest records |
| Documentation | Log sheets, test procedures, service reports and results kept on site | Files ready for auditors or health authorities |
CDC recommends offline cleaning and disinfection at least once a year and flushing low-flow pipe runs and dead legs at least weekly. If public health authorities suspect cases or an outbreak, the CDC guidance requires offline emergency cleaning and disinfection, with testing before and after remediation.
Which facilities need this programme?
Any facility with an open cooling tower or evaporative condenser should assess its risk, especially where many people are near the tower or the building air intakes:
- Hotels and resorts, where guests change constantly and towers often sit on roofs near public areas.
- Hospitals and clinics, where immunocompromised patients are more susceptible.
- Malls, offices and commercial buildings with cooling-tower-based HVAC.
- Factories, including food and beverage, chemicals, textiles and manufacturing, with process cooling towers.
- Power plants with large cooling towers whose drift can reach wide areas.
Building owners should check the Indonesian environmental health and occupational safety requirements that apply to their facility; this page does not replace applicable regulations.
What does Beta Pramesti Asia do?
Beta Pramesti Asia covers the water treatment side of the programme. The facility owner keeps the water management plan and its final decisions.
- Survey and water analysis. Review of the tower, basin, dead legs, injection points and water data; laboratory testing by A3 Laboratories through lab.id.
- Chemical programme. Oxidising and non-oxidising biocides, biodispersant, scale and corrosion inhibitors within the cooling tower chemical and HydroChem programmes.
- Cleaning and disinfection. Cooling tower cleaning service with a written procedure, waste handling and acceptance evidence before restart.
- Monitoring. Blowdown and dosing control with Sentinel CTS monitoring, plus auditable daily logs.
No programme can guarantee that a cooling tower is always free of Legionella. The aim is to suppress growth conditions, detect deviations early and keep a clear record of actions.
What should you send for an evaluation?
- Number, type and capacity of cooling towers, and their position relative to air intakes and public areas.
- System volume, circulation rate, water temperature and operating pattern (continuous, seasonal or often idle).
- Current chemical and biocide programme, dosing method and residual logs.
- Recent water and microbiology results, including Legionella results if any.
- Date of the last cleaning and disinfection and the condition of the basin, fill and drift eliminators.
Send the data through the Beta Pramesti contact page.
FAQ on Legionella in cooling towers
How do you prevent Legionella in a cooling tower?
Control biofilm and sediment, keep a measurable disinfectant residual, avoid stagnant water, control scale and corrosion, clean and disinfect the tower periodically, test the water in a laboratory and record every action. CDC and WHO place these steps in one water management programme.
Is a biocide alone enough?
No. Biofilm, sludge and scale shield bacteria from biocides. Biocides work together with biodispersant, physical cleaning, scale and corrosion control, and flow and blowdown management.
How often should a cooling tower be cleaned and disinfected?
CDC guidance recommends offline cleaning and disinfection at least once a year, plus before restart after a long idle period. The actual frequency is set from the risk assessment, test results and tower condition.
Does a negative Legionella result mean the tower is safe?
One negative result describes only the moment of sampling. Safety is judged from the testing trend, daily disinfectant residuals, cleanliness and how consistently the programme runs.
Who tests cooling tower water for Legionella?
A laboratory does. For cooling tower water testing, contact A3 Laboratories through lab.id and confirm the microbiology parameters, method and sample points before sampling.