Authored by: Rimkus Built Environment Solutions Marketing Team
Published 5/22/2026
A Centers for Disease Control and Prevention (CDC) review of 27 Legionnaires’ disease outbreaks investigated between 2000 and 2014 found that more effective water management programs might have prevented most of the outbreaks.
Cooling towers in commercial buildings are among the primary sources of Legionella exposure risk in workplaces. When maintenance lapses, the consequences can extend beyond equipment performance to include life safety concerns, regulatory violations, and significant financial exposure.
Key takeaways: Cooling tower maintenance responsibilities and risks for building owners
Cooling tower maintenance programs help protect building performance, occupant safety, and regulatory standing. The points below summarize what building owners and facilities directors need to know.
What matters most
- American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 180 splits duties between a “responsible party” (oversight) and an “implementing party” (execution), but delegation does not necessarily transfer the owner’s underlying accountability
- Poorly maintained cooling towers could promote Legionella growth, which the CDC links to approximately one in 10 diagnosed Legionnaires’ disease cases being fatal
- Jurisdictions including New York City and New York State require cooling tower registration, testing, and documented maintenance programs, with penalties up to $10,000 for noncompliance
How to approach cooling tower maintenance
- A written Water Management Program aligned with American National Standards Institute (ANSI)/ASHRAE Standard 188 is widely recognized as an industry benchmark for Legionella risk management
- Routine inspections, water treatment monitoring, and periodic offline cleaning and disinfection form the foundation of an effective program
- Regulatory requirements vary by jurisdiction; the trend is toward stricter enforcement and higher testing frequencies
Contact Us to speak with a qualified expert about cooling tower risk management.
What a cooling tower is and why maintenance matters
According to Environmental Protection Agency (EPA) WaterSense guidance, a cooling tower removes heat from a building’s cooling system by evaporating water. These systems serve office buildings, hospitals, hotels, manufacturing facilities, and other commercial properties where air conditioning or process cooling is required.
Because cooling towers continuously circulate water and expose it to air, their condition affects both system performance and health risk. That dual exposure is why routine maintenance is tied to energy use, water quality, and Legionella control.
How cooling towers operate
Warm water circulates over structured surfaces inside the tower while fans draw air across it. A portion of the water evaporates, pulling heat out of the remaining water before it returns to the building’s chiller or cooling system.
Why ongoing maintenance matters for performance and safety
Deferred maintenance could lead to mineral deposits on heat transfer surfaces, biological contamination, mechanical wear, and structural deterioration. Surface fouling might reduce heat transfer efficiency and drive up energy use over time. Stagnant or poorly treated cooling tower water may also create conditions where Legionella bacteria may grow and become airborne through the tower’s drift.
Who is responsible for cooling tower maintenance
The building owner generally carries primary responsibility for meeting commercial heating, ventilation, and air conditioning (HVAC) maintenance requirements, including cooling tower upkeep. The specific scope of that responsibility depends on applicable law, contract terms, and jurisdiction. Under ANSI/ASHRAE/Air Conditioning Contractors of America (ACCA) Standard 180-2018, the owner may designate other parties, such as property managers or maintenance contractors, to carry out operational duties. That delegation typically involves a formal contractual obligation and may not transfer the owner’s underlying accountability during a regulatory review, enforcement action, or outbreak investigation.
What effective cooling tower maintenance includes
A cooling tower maintenance program typically includes startup, routine operation, seasonal shutdown, and water treatment activities. Each phase addresses different risks and corresponds to relevant CDC guidance and applicable local regulations, while ASHRAE Standard 188 can provide the broader water management framework for these activities.
Together, these phases form the operational framework for controlling biological, chemical, and mechanical problems over the life of the system.
Startup maintenance
When a cooling tower remains offline for more than five days, industry guidance calls for cleaning and disinfection before returning it to service. Operators apply disinfection treatment before circulating water through the heat transfer surfaces or operating fans to limit the risk of aerosolizing concentrated bacteria.
Routine inspection and operational checks
ASHRAE Standard 180 establishes minimum inspection frequencies for commercial cooling tower components. Monthly tasks typically include water treatment analysis, chemical testing, and microbiological treatment. Quarterly and semiannual checks cover mechanical components, water droplet capture devices, internal heat transfer material, and structural members.
Water treatment and chemistry management
Water chemistry control addresses four primary treatment concerns in cooling systems: mineral scale, corrosion, fouling, and biological growth. EPA guidance on cooling tower water management discusses regular monitoring of water quality and treatment conditions. Maintaining appropriate disinfectant levels as part of a water management program is a CDC-recommended control measure for Legionella risk.
Shutdown and seasonal maintenance
CDC guidance recommends taking cooling towers offline for cleaning and disinfection at least annually. These shutdown activities should be documented in the building’s overall water management program.
Common cooling tower issues
Cooling towers may develop a recurring set of problems over time: biological growth, scaling, corrosion, leaks, overflows, drift, and gaps in routine operation. Each issue has its own warning signs and consequences for performance and safety, as outlined in Department of Energy (DOE) Federal Energy Management Program (FEMP) materials.
Biological growth and Legionella risk
Cooling towers can promote bacterial growth in warm, moist conditions, particularly within the 77 to 113°F range. Legionella bacteria may thrive in the slimy biological layer (biofilm) that forms on basin walls and fill media (the structured material inside the tower that increases water-to-air contact) when disinfectant levels drop. Occupational Safety and Health Administration (OSHA) guidance notes that cooling towers can create conditions favorable to Legionella growth and aerosolization if not properly maintained.
Scale, corrosion, and fouling
As water evaporates, dissolved minerals concentrate in the recirculating water and deposit on heat transfer surfaces, fill, and piping. Corrosion produces rust staining and pitting on metal surfaces, while fouling from suspended particles creates dry spots on fill surfaces and distorted spray patterns. In severe cases, scale buildup may contribute to damage in portions of the tower fill or structure.
Mechanical and structural deterioration
Fan blade cracks, corroded bearings, and worn drive belts can reduce airflow and heat rejection capacity over time. Long-term environmental exposure might also weaken structural members, fasteners, and basin walls, especially in coastal or harsh-climate locations.
Drift, water loss, and efficiency decline
Without water droplet capture devices (called drift eliminators), water loss can range from 0.05% to 0.2% of recirculating flow. Cooling towers can also account for 20 to 50% of total facility water use. Uncontrolled loss may become a significant operating cost over time.
Signs of cooling tower problems
Cooling tower deterioration may produce visual, performance, and water quality indicators that might signal treatment failures or mechanical degradation before they escalate. Early identification may allow building owners to address deficiencies before they affect occupant safety or trigger regulatory action.
Visual and structural indicators
Visible scale deposits, rust staining, and algae growth on basin walls may indicate chemical or biological treatment failures. Sagging or warped fill, standing water in areas not intended to remain wet, and deteriorated structural members may indicate conditions that warrant prompt evaluation.
Performance and water quality indicators
Rising energy costs without corresponding load changes, reduced cooling capacity, and higher condenser water temperatures may point to fouling, scale accumulation, or mechanical degradation. Shifts in pH, increased conductivity, loss of disinfectant residual, and elevated bacterial counts in routine water samples indicate the water treatment program is not maintaining adequate control.
Regulatory and compliance considerations for cooling towers
Cooling tower regulations have intensified following several documented Legionnaires’ disease outbreaks. Building owners now face a layered set of obligations: federal workplace safety requirements, voluntary national standards that some local laws adopt by reference, and municipal ordinances with specific testing and reporting mandates.
Because these obligations vary by location, compliance often depends on both the broader water management framework and the specific registration, testing, and reporting rules in the building’s jurisdiction. That combination could make documentation and clearly assigned responsibility especially important.
ASHRAE 188 and Legionella risk management
ANSI/ASHRAE Standard 188 establishes minimum Legionella risk management requirements for building water systems. Any building that meets ASHRAE 188 coverage criteria and has a cooling tower must develop a written Water Management Program that identifies responsible persons, documents maintenance and treatment requirements, and includes a response plan for suspected Legionella cases.
At the federal level, the standard is voluntary. OSHA’s General Duty Clause, however, requires employers to address recognized workplace hazards, and failure to follow ASHRAE 188 can serve as evidence of an unaddressed hazard even in jurisdictions without specific cooling tower legislation.
State and municipal cooling tower ordinances
Several jurisdictions have enacted mandatory cooling tower regulations. NYC Local Law 77, enacted after a 2015 Legionnaires’ disease outbreak that sickened 138 residents and caused 16 deaths, requires cooling tower registration, a documented maintenance program complying with ASHRAE 188, and annual certification. In May 2026, NYC increased its Legionella testing requirement from every 90 days to every 31 days. Failure to register or certify can result in penalties up to $10,000.
New York State’s 10 NYCRR Part 4 applies statewide, requiring registration, 90-day inspections by licensed professionals, and 24-hour reporting of Legionella results exceeding 1,000 CFU/mL. Other jurisdictions have adopted their own requirements. Building owners operating outside regulated jurisdictions still face potential risk exposure under the OSHA General Duty Clause, and voluntary adoption of ASHRAE 188 may help demonstrate alignment with an established Legionella risk-management framework.
How professional condition assessments may support cooling tower risk management
Cooling tower maintenance programs address biological, chemical, mechanical, and structural risks that affect building performance, occupant safety, and regulatory compliance. A written Water Management Program aligned with ASHRAE 188, supported by documented inspection and testing records, could serve as both an operational management tool and a record relevant to enforcement or investigation.
For building owners and facilities directors managing aging cooling tower systems or navigating jurisdiction-specific compliance obligations, a professional condition assessment may help identify mechanical deficiencies, structural deterioration, and potential program gaps before they escalate.
Contact Rimkus to discuss cooling tower evaluations and mechanical engineering consulting for commercial building systems.
Frequently asked questions about cooling tower maintenance
How do I know if my cooling tower has a Legionella problem?
Several indicators may signal a Legionella control problem in a cooling tower system: disinfectant residual readings that fall below target levels between service visits; microbiological test results showing elevated bacterial counts; visible biofilm, slime, or algae growth on basin walls or fill media; water temperatures in the range associated with Legionella growth (77 to 113 degrees Fahrenheit); and any confirmed Legionnaires’ disease case in the building or nearby area where the tower is identified as a potential source. Routine microbiological testing is the primary detection tool. Under NYC’s updated regulations effective May 2026, Legionella culture sampling is required at least every 31 days during operation. New York State requires sampling at intervals not exceeding 90 days. Outside regulated jurisdictions, ASHRAE Standard 188 Water Management Program protocols provide the recognized framework for routine monitoring.
What are the penalties for non-compliance with NYC’s cooling tower regulations?
Under NYC Local Law 77, as amended by Local Law 159 of 2025, civil penalties for cooling tower violations start at up to $2,000 for a first violation and up to $5,000 for subsequent violations. Where a violation is accompanied by or results in a fatality or serious injury, the penalty can reach $10,000. Failure to comply with an abatement order is a misdemeanor punishable by a fine of up to $25,000 or imprisonment of up to one year. Failure to register or certify can also result in penalties. Beginning May 2026, the law also increased fines for non-compliance with the new 31-day testing requirement. Building owners outside NYC still face potential exposure under OSHA’s General Duty Clause if they fail to address recognized Legionella hazards.
Does my building need a Water Management Program?
It depends on where your building is located and whether it meets ASHRAE Standard 188 coverage criteria. Under ASHRAE 188, any building with a cooling tower that meets the standard’s applicability criteria must develop a written Water Management Program identifying responsible persons, documenting maintenance and treatment requirements, and including a response plan for suspected Legionella cases. In New York City, a documented maintenance program complying with ASHRAE 188 is required by law under Local Law 77. New York State’s 10 NYCRR Part 4 applies a similar requirement statewide. At the federal level, ASHRAE 188 is voluntary, but OSHA’s General Duty Clause requires employers to address recognized workplace hazards. Failure to follow ASHRAE 188 can serve as evidence of an unaddressed hazard. For building owners outside regulated jurisdictions, voluntary adoption of a written Water Management Program aligned with ASHRAE 188 may help demonstrate a proactive approach to Legionella risk management.
This article is intended to provide general information and insights into prevailing industry practices. It is not intended to constitute, and should not be relied upon as, legal, technical, or professional advice. The content does not replace consultation with a qualified expert or professional regarding the specific facts and circumstances of any particular matter.