A cooling tower is the one piece of HVAC equipment in your building that can make the news. It sprays warm water into the air — and warm water plus biofilm is exactly what Legionella bacteria need. The maintenance program isn't about comfort; it's about keeping a public-health story from ever having your building's name in it.
Why the cooling tower is a public-health asset, not just an HVAC one
Most HVAC equipment failures are a comfort or cost problem. A cooling tower failure can be a health and liability problem. Here's the mechanism, in plain terms: the tower rejects heat from the building's chiller by evaporating water. That means it holds a reservoir of warm water (25–45°C — the ideal Legionella growth range) and produces a fine mist that can drift off the tower. If the water grows Legionella and the mist carries it where people breathe, you have the conditions behind Legionnaires' disease outbreaks.
That's why cooling tower maintenance is held to a different standard than, say, boiler maintenance. The goal of the water program is twofold: keep the equipment efficient, and keep the water biologically controlled so the mist is never a hazard.
Where Ontario stands on cooling tower regulation
This is the question property managers ask first, so let's be clear and careful: Ontario does not currently have a single province-wide cooling tower registration-and-testing law of the kind that exists in some jurisdictions (Quebec's RBQ program and New York City's local law are the well-known examples). What Ontario building owners do have is a general duty of care, and local public health units with the authority to investigate and order remediation after a cluster of cases.
In practice, that means the well-run buildings don't wait for a law. They operate a documented Legionella risk management plan voluntarily, because:
- The cost of the program is a few thousand dollars a year.
- The cost of an incident — investigation, remediation, legal exposure, insurance consequences, and a building's name attached to a health story — is in a different universe entirely.
- A documented program is the single best evidence of due diligence if anything ever happens.
Regulations change. This guide reflects the general landscape as of 2026 and is not legal advice. Confirm current requirements with your local public health unit and your condo's legal counsel before setting your program. The direction of travel across North America is toward more cooling-tower regulation, not less — building a documented program now means you're ahead of it.
What a real cooling tower water-treatment program covers
A proper program runs on three control levers, continuously balanced by a water-treatment specialist:
1. Biocide control (the Legionella lever)
Oxidizing and non-oxidizing biocides are dosed to keep microbiological activity suppressed. The program tracks biocide residual and microbiological counts so the water never becomes a growth medium. This is the control that matters most for health.
2. Scale and corrosion control (the efficiency lever)
Minerals in make-up water concentrate as water evaporates. Left uncontrolled, they scale the condenser and tower fill — and a scaled condenser makes the chiller work 10–20% harder for the same cooling. Corrosion inhibitors protect the metal. This is the control that protects your energy bill and your chiller's lifespan.
3. Cycles of concentration (the water-cost lever)
"Cycles of concentration" is how many times water is reused before being drained (blown down) and replaced. Running higher cycles — 6 instead of 3 — means less water sent to the sewer and less make-up water consumed, cutting water, sewer, and chemical costs. The limit is scaling risk, which is why cycles are tuned against live water chemistry, not set and forgotten.
The dangerous gap in most cooling tower programs is the time between tests. A weekly manual reading can't catch a biocide pump that failed on Tuesday. Continuous monitoring of conductivity, biocide residual, and tower temperature — surfaced on a mechanical dashboard with alerts — closes that gap, so a water-treatment problem pings the manager the hour it starts, not at the next scheduled visit.
The seasonal rhythm of a GTA cooling tower
Toronto's climate means towers run hard in summer and sit idle in winter — and a stagnant idle tower is itself a Legionella risk if it isn't handled properly. The annual rhythm:
| Season | Key cooling tower tasks |
|---|---|
| Spring startup (Apr–May) | Clean basin & fill, disinfect, inspect drift eliminators, recommission water treatment, baseline testing |
| Operating season (May–Sep) | Continuous/weekly testing, monthly treatment review, Legionella sampling per plan, cycles optimization |
| Mid-season check (Jul–Aug) | Inspect fill condition, verify biocide dosing, clean strainers, confirm drift eliminator integrity |
| Fall shutdown (Oct) | Drain, clean, disinfect, dry lay-up (or wet lay-up protocol if required), document condition |
The two bookends — startup and shutdown cleaning — are non-negotiable. A tower that's drained dirty in the fall and refilled onto that same biofilm in the spring has given Legionella a head start before the season even begins.
What cooling tower maintenance costs in the GTA (2026)
| Item | 2026 Cost |
|---|---|
| Full-season water treatment program (per tower) | $6,000 – $18,000 / yr |
| Seasonal cleaning (startup + shutdown) | $2,500 – $6,000 |
| Legionella culture sampling (per test) | $120 – $280 |
| Drift eliminator replacement | $4,000 – $12,000 |
| Fill media replacement | $12,000 – $22,000 |
| Cooling tower replacement (250 tons) | $85,000 – $145,000 |
Put the program cost in context: a full season of water treatment and testing is a rounding error against the efficiency loss from a scaled chiller alone. A condenser running 15% less efficiently on a 400-ton water-cooled plant can quietly add tens of thousands to the summer hydro bill — more than the entire water program costs. And that's before you price in what a single Legionella incident would mean.
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Request a Free Review →A cooling tower compliance checklist for your board
- Do you have a written Legionella risk management plan for the building? If not, that's step one.
- Is water treatment a continuous professional program, not just periodic visits?
- Is Legionella sampling done on a documented cadence during operating season?
- Are startup and shutdown cleanings contracted and documented every year?
- Is there alerting if biocide dosing or water chemistry drifts out of range between tests?
- Is every test, cleaning, and sample result logged and retained as your due-diligence record?
If you can answer yes to all six, your building is ahead of most in the GTA — and ahead of where regulation is heading. If you can't, those are the exact gaps to close before next cooling season.
Frequently Asked Questions
How often should a cooling tower be cleaned and tested in Ontario?
Test water continuously or at least weekly in operating season (conductivity, biocide residual, pH), with a monthly professional review. Clean and disinfect the basin and fill at spring startup and fall shutdown, plus a mid-season check. Legionella sampling cadence follows your risk plan — monthly during operation is a common benchmark.
Is Legionella testing required by law for cooling towers in Ontario?
Ontario has no single province-wide cooling tower testing law as of 2026, but owners carry a duty of care and public health units can order remediation after a case. Most well-run buildings run a documented risk management plan voluntarily. Confirm current rules with your public health unit and legal counsel.
What are cycles of concentration?
It's how many times tower water is reused before being drained and replaced with fresh make-up water. Higher cycles save water, sewer, and chemical costs; the limit is scaling and corrosion risk, which a water-treatment program balances against live chemistry.
What does cooling tower maintenance cost for a GTA building?
A full-season program runs $6,000–$18,000 per tower per year in 2026; seasonal cleaning is $2,500–$6,000. It's small against the cost of a scaled, inefficient chiller — or a Legionella incident.