Short answer: preventing Legionella in a cooling tower requires a water management programme that controls sediment/biofilm, temperature, water age, and disinfectant residual. Set site-specific control limits, assign monitoring and response owners, clean and disinfect on schedule, and escalate Legionella results together with operating trends—not from one test result in isolation.
Last technically reviewed: 17 July 2026.
Legionella can grow in warm water and spread through cooling-tower aerosols. This matters in Indonesia because cooling towers serve commercial buildings, hospitals, power generation, mining, petrochemical, pulp and paper, and other process plants. An effective programme protects workers, occupants, neighbouring communities, and operational continuity.
CDC guidance updated on 3 January 2025 groups the main factors under STAR: sediment and biofilm, temperature, water age, and disinfectant residual. CDC also notes that both open- and closed-circuit towers can release aerosols and need the same basic operation and maintenance protocols (CDC: Controlling Legionella in Cooling Towers).
Understanding Legionella Risk in Cooling Towers
The highest risk occurs when favourable growth conditions, aerosol exposure, and failed controls coincide. Map water from make-up through basin, pump, heat exchanger/condenser, headers, active and standby cells, bypasses, side-stream filter, injection points, and blowdown—including concealed low-flow pipework.
| Risk point | Why it matters | Evidence to inspect | Main control |
|---|---|---|---|
| Basin and remote sump | Sediment, warm water, and sludge support biofilm | Photographs, deposit inspection, temperature, cleaning history | Cleaning, circulation, drainage, biocide programme |
| Fill pack, drift eliminator, nozzle | Large wet area; fouling disrupts distribution and can increase drift | Visual inspection, pressure/flow distribution, eliminator condition | Cleaning, component replacement, scale/corrosion control |
| Dead leg, bypass, standby cell | Water age rises and disinfectant residual may disappear | P&ID walkdown, valve position, flushing record | Remove dead legs where possible; scheduled flushing and circulation |
| Make-up and side-stream points | Introduce solids, nutrients, and organisms; filtration can fail | Make-up quality, filter differential pressure, turbidity/TSS | Pretreatment, filtration, maintenance |
| Aerosol zone and air intake | Drift may enter ventilation or expose workers | Separation/orientation, prevailing wind, eliminator condition | Drift elimination, placement, access control/PPE during work |
| Dosing and sensors | Feed loss or sensor drift removes a barrier | Tank level, pump calibration, residual trend, alarm history | Automation, interlock, calibration, duty/standby |
CDC describes 25–45°C as the most favourable Legionella growth range and recommends operating at the lowest practical water temperature. Temperature alone does not prove control: biofilm, stagnation, sediment, and disinfectant residual must be evaluated together.
Best Practices for Legionella Prevention in Cooling Towers
An effective programme combines prevention, verification that tasks were completed, and validation that controls work. ANSI/ASHRAE Standard 188-2021 establishes minimum legionellosis risk-management requirements for building water systems, while ASHRAE Guideline 12 supports implementation (ASHRAE Standard 188-2021).
1. Risk Assessment
The water management team should map the system, potentially exposed populations, normal and standby conditions, seasonal changes, test history, and corrective actions. Include operations, maintenance, HSE, engineering, the facility owner, water-treatment service, and microbiology/laboratory competence.
Repeat the assessment after commissioning, retrofit, make-up-water or chemical changes, prolonged shutdown, worsening Legionella indicators, or a suspected illness. State who approves control limits and who can stop operation or order remediation.
2. Proper Design and Construction
Design should reduce stagnation, permit complete drainage and cleaning, provide safe access to basins/fill/nozzles, and use high-efficiency drift eliminators. CDC recommends avoiding dead legs, circulating water during intermittent operation, and installing an automated water-treatment system.
For new projects, review tower placement relative to air intakes, public areas, and work routes. For an existing tower, walk down the P&ID to find bypasses, equaliser lines, standby cells, remote sumps, and branches that lose circulation at partial load.
3. Comprehensive Maintenance Program
Maintenance should combine condition-based tasks with documented minimum intervals. CDC recommends offline disinfection and cleaning at least annually, with more frequent work when environmental load, deposits, or performance indicators warrant it. Follow-up must verify deposit removal, equipment function, and stable chemical control.
Use work orders for fill, nozzles, strainers, basin, drift eliminators, heat exchangers, side-stream filters, sensors, dosing pumps, valves, and standby components. When deposits cannot be controlled online, plan a cooling-tower cleaning service with isolation, waste handling, and post-work evidence.
4. Effective Water Treatment
Chemical treatment must control microbiology without neglecting scale, corrosion, sediment, and material compatibility. Keep oxidising disinfectant measurable throughout each day within the product label and programme limits; dose non-oxidising products to the approved concentration and contact time.
Betagard Cooling Tower Chemicals cover biocides, inhibitors, dispersants, dosing, and monitoring. Product and dose selection must follow water analysis, metallurgy, cycles of concentration, organic load, microbiology, the SDS/label, and discharge permits—not a setpoint copied from another tower.
5. Monitoring and Testing
Monitoring links a control limit to action. Increase frequency when values become unstable, following an operating change, or during remediation. CDC does not specify one Legionella test schedule for every facility; the sampling plan should reflect its purpose, representative points, laboratory method, baseline, and population risk.
| Parameter / evidence | Control limit | Initial frequency | Data owner | Escalation when out of limit |
|---|---|---|---|---|
| Disinfectant residual | Product- and site-specific range | Online/daily according to stability | Water-treatment operator | Verify sensor and pump feed; correct per SOP; increase sampling |
| pH and conductivity/CoC | Programme and material limits | Online/shift/daily | Operations/utilities | Inspect blowdown, make-up, dosing, and calibration |
| Temperature and stagnation | As low as practical; dead legs/standby per flush plan | Daily + weekly inspection | Operations/maintenance | Restore circulation, flush, review cell sequencing |
| Turbidity/TSS, sediment, biofilm | Baseline/trend and inspection criteria | Weekly/monthly by risk | Water treatment + maintenance | Inspect basin/filter; clean or correct filtration |
| Legionella culture | WMP performance indicator; CDC: <10 CFU/mL indicates better control, ≥10 requires review/response | Risk-based sampling plan | HSE + competent laboratory | Confirm chain of custody; review WMP; correct and retest |
| Alarms, calibration, work orders | No open critical alarm; calibration on time | Weekly/monthly review | Utilities supervisor | Assign owner and due date; assess interim operating risk |
CDC values are performance indicators, not a “safe level” and not a prediction of illness. Results should be interpreted with concentration, trend change, colonisation extent, species/serogroup, and facility conditions; CDC states that there is no known safe Legionella level (CDC: Routine Testing for Legionella).
Programme validation evidence matrix
Validation proves that the programme is controlling risk, not only that tasks were completed. Use this matrix when Legionella, biofilm, residual, or physical-condition evidence starts moving away from baseline.
| Validation evidence | Sign that control is improving | If it is not improving |
|---|---|---|
| Repeat Legionella results at the same point | Trend falls or remains below the WMP response limit after corrective action | Check chain of custody, sample point, colonisation extent, species/serogroup, and remediation need |
| Disinfectant residual and pH | Residual stays within the product range and pH supports its effectiveness | Calibrate sensors, check water demand, tank level, dosing pump, and injection point |
| Biofilm/sediment inspection | Basin, fill, nozzles, and strainers remain clean after restart | Schedule cooling-tower cleaning, side-stream filtration, or source-solids correction |
| Water balance and water age | Standby cells, bypasses, and dead legs have recorded flushing or circulation | Revise cell operation, remove dead legs where practical, and audit valve position |
| Response records | Corrective action closes with owner, date, photo/data, and approval | Escalate to HSE/engineering because the deviation has not been closed with evidence |
6. Comprehensive Water System Management
At minimum, the programme should include a system diagram, team and responsibilities, hazard analysis, control limits, monitoring methods, corrective actions, verification, validation, communications, and record retention. Close each deviation with evidence rather than a note that it was “fixed”.
In Indonesia, Ministry of Health Regulation No. 2 of 2023 is the current general environmental-health implementation framework and revoked Regulation No. 32 of 2017. For hospitals, Ministry of Health Regulation No. 7 of 2019 contains cooling-tower Legionella provisions, although its environmental-media standards were partially revoked by Regulation No. 2 of 2023. Each facility should confirm current scope, permits, and sector/local requirements with its HSE/legal function.
7. Use of Innovative Technology
Technology adds value when it closes a mapped risk. Automated residual, pH, conductivity, flow, and chemical-level monitoring can shorten detection time; Betaqua Sentinel CTS supports those operating trends. Sensors still need correct sample locations, calibration, maintenance, and an alarm response.
Side-stream filtration or make-up pretreatment such as ultrafiltration can reduce incoming solids and organisms, but neither replaces the tower water management programme. UV also leaves no residual across the loop; biofilm, dead legs, and recontamination still require other controls.
8. Source Water Management
Make-up water determines the solids, nutrients, organisms, and chemical demand entering the tower. Monitor source changes, turbidity/TSS, hardness, alkalinity, chloride, silica, organics, and relevant microbiology. Reuse water or condensate needs a separate hazard review before adoption as make-up.
Select pretreatment for the demonstrated problem: clarification/filtration for solids, softening or RO for selected minerals, and disinfection for the assessed risk. Do not increase cycles of concentration without calculating the effects on scale, corrosion, disinfectant residual, and the blowdown permit.
9. Energy and Water Management
Water efficiency must not increase water age or reduce blowdown outside control limits. Optimise cycles of concentration while keeping chemistry, solids, and microbiology within the approved range. Cell sequencing should balance energy savings with circulation through standby cells.
Trend make-up, blowdown, estimated evaporation, conductivity, heat load, and fan/pump operation together. A water-balance anomaly may indicate leakage, valve error, excess drift, or sensor failure—all relevant to operation and exposure risk.
10. Emergency Preparedness and Response
The response plan should distinguish a control deviation, worsening routine test, suspected illness, and an outbreak declared by public health. Define command, shutdown authority, area restriction, communication, sampling, contractor access, PPE/respiratory protection, waste handling, and return-to-service criteria.
For suspected illness or outbreak, coordinate with public health before sampling and remediation. CDC recommends offline emergency cleaning and disinfection when the authority having jurisdiction suspects associated illness. Adapt the procedure to materials, volume, configuration, chemical label, worker safety, and discharge rules.
Cleaning and disinfection records to retain
- Tower/cell ID, date, reason for work, pre-shutdown operating condition, and person in charge.
- Photographs/findings for basin, fill, nozzles, drift eliminator, strainer, dead legs, and accessible heat exchangers.
- Chemical and batch/lot, target and actual concentration, pH, contact time, temperature, and test instrument.
- Isolation sequence, fan/pump status, area restriction, PPE, and disposal route.
- Rinse result, post-work inspection, sensor calibration, restart checklist, and new residual/chemistry baseline.
- Pre- and post-work Legionella results when required, including method, location, time, laboratory, and chain of custody.
- Corrective action, owner, due date, verification, and return-to-service approval.
Conclusion
Legionella control is a repeating management system, not a one-off dose or cleaning visit. The risk map shows where growth and aerosol spread can occur; control limits provide signals; action owners close deviations; and records demonstrate whether the programme was implemented.
PT Beta Pramesti Asia can support water-chemistry review, a cooling-tower biocide programme, monitoring, and cleaning scope. Public-health decisions, clinical diagnosis, and outbreak declarations remain with qualified health professionals and the relevant authority.
Questions and Answers
Q1: Why are cooling towers in Indonesia at high risk of Legionella growth?
Cooling towers create aerosols and contain wet surfaces, basins, and circulation networks that may hold warm water, biofilm, sediment, or stagnation. A tropical climate can extend warm conditions, but each facility’s risk still depends on design, operation, make-up quality, maintenance, and water management programme effectiveness.
Q2: How can the use of technologies such as ultrafiltration help in the control of Legionella in cooling towers?
Ultrafiltration on make-up water can reduce incoming particles and microbial load when correctly designed and operated. It does not control growth in the basin, fill, dead legs, or loop after recontamination, so it must be combined with circulation, cleaning, corrosion/scale control, disinfectant residual, and validation.
Q3: What is the role of automated monitoring in Legionella prevention in cooling towers?
Automated monitoring gives earlier warning when disinfectant residual, pH, conductivity, flow, or chemical level leaves its range. It does not directly measure the complete Legionella risk. Sensors need calibration, manual cross-checks, representative placement, and a time-bound operator response.
References
- CDC, Controlling Legionella in Cooling Towers, updated 3 January 2025.
- CDC, Routine Testing for Legionella, updated 3 January 2025.
- ANSI/ASHRAE Standard 188-2021, Legionellosis: Risk Management for Building Water Systems.
- Indonesia Ministry of Health Regulation No. 2 of 2023 implementing Government Regulation No. 66 of 2014 on Environmental Health.
- Indonesia Ministry of Health Regulation No. 7 of 2019 on Hospital Environmental Health, including the partial-revocation status recorded by BPK.