In May 2026, Hamilton Public Health found a cluster of Legionella cases in East Hamilton and Stoney Creek. The first reports listed 13 cases. That number grew to 19 people in hospital as the probe went on. No common source has been named yet. But cooling towers and other warm-water systems are being checked.
If you look after a building's water in Ontario, this is a good time to check your own setup. Don't wait for illness to force the issue.
How Legionella spreads
Legionella is a germ found in water. It grows fast in warm, still water. The danger zone is 25ยฐC to 45ยฐC.
People get sick by breathing in tiny water droplets. They do not get sick by drinking the water. That's why the worst risks are cooling towers, fountains, hot tubs, humidifiers, and misting systems. Large hot water systems can also be a risk. Dead legs and unused taps are the main weak spots.
The illness is called Legionnaires' disease. It is a bad form of pneumonia. Hamilton Public Health says some groups face more risk. These include adults over 50, smokers, and people with weak lungs or weak immune systems. The signs are fever, chills, cough, and short breath. They look like many other chest bugs. That is why outbreaks can spread before doctors see the link.
Why you can't spot it without tests
You can't see, smell, or taste Legionella in water. Most cases are found only after someone ends up in hospital. By then, other people have likely been exposed too.
Tests flip the script. Take samples from cooling tower basins, hot water tanks, and far-end taps. This can find the germ weeks or months before it makes anyone sick. It also catches it long before your building shows up in the news.
What a water plan should cover
A written plan is what sets "we do upkeep" apart from a strong record on paper. The key parts:
- Test for Legionella each quarter at set points. Test more often for cooling towers in use.
- Keep hot water above 60ยฐC at the tank and 55ยฐC at the tap. Keep cold water below 20ยฐC.
- Flush taps that don't get much use. This stops water from sitting still.
- Clean and treat cooling towers on the maker's schedule, and before each season.
- Write down each test, each reading, and each fix.
Hamilton Public Health has told cooling tower operators that gaps in upkeep are how most outbreaks start.
Which buildings should care most
Risk goes up with two things. How big and complex the water system is. And how at-risk the people in the building are. Long-term care homes and hospitals score high on both. Hotels, condo towers, schools, and large offices come next. Any place with tall pipe stacks, rooftop cooling towers, or pipe runs that don't see daily use is in this group.
Old pipes raise risk too. Scale, grime, and slime inside them give germs a place to grow.
The bottom line
The Hamilton cases are still being looked at. The source may take time to find. But the pattern is always the same: silent growth, sick people, then a rush to find the cause. The buildings that stay out of the news are the ones that test, write things down, and fix small issues first.
Has it been more than a year since you tested your water? Do you have a written plan? If not, now is the time.
For Legionella testing and water compliance support in Ontario, contact Canadian Water Compliance.
Sources: Hamilton Public Health, CBC Hamilton, CHCH News.
