Most building owners with cooling towers understand them at a surface level. Water goes up, heat goes out, the building stays cool. The mechanical reality is more specific than that, and the maintenance stakes are considerably higher.
Skip cooling tower water treatment and you are not just losing efficiency. You are creating conditions under which Legionella bacteria can colonize the system and be aerosolized into the surrounding environment. According to the Centers for Disease Control and Prevention (CDC), Legionnaires' disease kills roughly one in ten people it infects. The regulatory framework around cooling tower maintenance exists because of documented outbreaks tied to neglected systems, and Michigan's requirements are specific and enforceable.
None of that is alarmist framing. Properly maintained cooling towers do not cause Legionella outbreaks. The standard for maintenance is high because the consequences of not meeting it are severe.
Heat Rejection: What the Tower Is Doing
A cooling tower is a heat rejection device. In a water-cooled chiller system, the chiller absorbs heat from the building and transfers it to condenser water. That warm condenser water pumps to the cooling tower on the roof, where it is distributed over fill media and exposed to airflow. A portion of the water evaporates, and evaporation carries heat away from the remaining water. The cooled water returns to the chiller to absorb more heat and the cycle continues.
The evaporation is what makes cooling towers efficient at heat rejection. It is also what creates the water quality problem.
As water evaporates, it leaves dissolved minerals behind. Those minerals concentrate in the system water over time. Calcium and magnesium carbonate deposits form scale on the heat transfer surfaces of the chiller's condenser tubes, the tower fill media, and distribution nozzles. Scale is an effective insulator. A scaled condenser tube forces the chiller to work harder to reject the same amount of heat, degrading efficiency and stressing the compressor.
The evaporation also means the system is constantly losing water volume. That water is replaced by makeup water, which introduces fresh dissolved minerals into an already-concentrated system. Managing the mineral concentration, called cycles of concentration, through controlled blowdown, is a core water treatment function.
Where Legionella Enters the Picture
Legionella pneumophila is a naturally occurring bacterium found in freshwater environments. It becomes dangerous when it colonizes engineered water systems and achieves concentrations high enough to be inhaled as an aerosol. Cooling towers create exactly the conditions under which this can happen: warm water, a humid environment, a nutrient supply from accumulated organic matter, and a mechanism for generating aerosol droplets that can travel in air.
Legionella grows most aggressively between 77 and 113 degrees Fahrenheit, which overlaps with the operating temperature range of cooling tower basin water. Below 68 degrees it becomes dormant. Above 131 degrees it dies quickly. The condenser water in an operating cooling tower does not typically reach lethal temperatures on its own. Without active management, it stays exactly in the range where Legionella grows. A cooling tower without a water treatment program creates and sustains the conditions under which a Legionella outbreak can develop. The public health consequences are severe enough that regulators treat prevention as mandatory, not advisory.
What Water Treatment Actually Involves
A proper cooling tower water treatment program has several components that work together.
Biocide treatment to control microbial growth, including Legionella. This typically involves oxidizing biocides such as chlorine or bromine applied on a continuous or intermittent basis, combined with non-oxidizing biocides on a rotating schedule to prevent resistance development. The biocide program requires regular water sampling and analysis to verify that target disinfection levels are being maintained. It cannot be set up once and left alone.
Scale and corrosion inhibitors to manage mineral deposition and protect metal components. Scale on condenser tubes costs real money in chiller efficiency every operating hour. Corrosion of basin and tower components creates maintenance problems and potential water quality issues from corrosion products entering the system.
Blowdown management to control cycles of concentration. As minerals concentrate in the system, the water must be partially discharged and replaced with fresh makeup water to keep mineral levels in range. Automated blowdown controllers measure conductivity as a proxy for mineral concentration and discharge water when the setpoint is exceeded.
Physical cleaning. The fill media, basin, distribution nozzles, and drift eliminators need periodic physical inspection and cleaning. Biofilm can establish on surfaces faster than chemical treatment alone can eliminate it, and a biofilm matrix protects bacteria from biocide contact. Annual cleaning combined with chemical treatment is the standard approach.
Michigan's Regulatory Requirements
Michigan requires buildings with cooling towers to maintain a written water management plan that addresses Legionella risk. The plan must document the system, identify risk control measures, establish monitoring and response procedures, and be reviewed and updated regularly. Buildings that cannot produce that documentation are carrying regulatory exposure.
"We treat the water" is not a sufficient answer to a compliance question. The question is whether the treatment is documented, whether monitoring is occurring at the required frequency, and whether the water management plan actually reflects the current system.
Seasonal Maintenance by the Calendar
Spring startup before cooling season: full physical inspection of basin, fill, nozzles, and drift eliminators. Cleaning if needed. Verification of chemical feed equipment. Startup of the water treatment program with initial water analysis. Review of the water management plan.
Ongoing through cooling season: monthly water sampling and analysis at minimum. Biocide residual verification. Conductivity monitoring and blowdown adjustment. Visual inspection of tower condition. Documentation of all readings and actions.
Fall shutdown: system draining or winterization depending on climate exposure. Physical cleaning if not done at startup. Documentation of shutdown condition and any maintenance needs identified for spring.
Annual: comprehensive review of the water management plan. Third-party water analysis if internal testing shows anomalous results. Physical inspection of all components including drift eliminators, which are critical for limiting aerosol release. If your current cooling tower maintenance program does not cover all of that, the gaps are worth closing before cooling season begins. We maintain cooling towers alongside the rest of the mechanical system for commercial buildings across Southeast Michigan. The water treatment conversation is one we would rather have proactively than in response to a regulatory notice.
maintenance plans, 24/7 service, and system replacement across Southeast Michigan. Call (248) 590-0010 or reach out at sales@vitalitymechanical.com.