When someone gets sick from Legionnaires’ disease inside a building, the first question lawyers ask is not who turned on the faucet. It is who controlled the water system. Legionnaires’ disease is a severe form of pneumonia caused by the Legionella bacterium. That bacterium lives in warm water. It thrives in cooling towers, hot water tanks, decorative fountains, shower heads, and even the pipes behind a hotel room wall. The disease spreads when people breathe in water vapor contaminated with the bacteria. It does not spread from person to person. That means the source is almost always a physical property condition. And that means property owners and managers are the ones who face legal claims when an outbreak occurs.
The legal theory behind these claims is not complicated. If you own or manage a building, you have a duty to keep it reasonably safe for people who enter it. That duty extends to the water you provide. A tenant, guest, or employee who contracts Legionnaires’ disease because of a neglected water system has a strong case for negligence. To win, the injured person must show that you knew or should have known about the risk, that you failed to take reasonable steps to fix it, and that this failure caused their illness. In plain terms, if you ignore a building’s water quality, you are setting yourself up for a lawsuit.
What does “reasonable steps” actually mean? Courts do not expect a property owner to be a microbiologist. But they do expect you to act on what a reasonable person in your position would know. For example, if you manage a large apartment complex with a recirculating hot water system, you need to know that Legionella grows when water temperatures stay between 77 and 108 degrees Fahrenheit. You also need to know that stagnant water, scale, and biofilm inside pipes create a perfect breeding ground. A property owner who lets hot water sit in the “danger zone” and does nothing to flush the system is acting negligently. So is an owner who ignores a positive test result from a water sample. If you know the bacteria is there and you do not disinfect, you are not just careless. You are willfully indifferent to the safety of the people who live or work in your building.
The most common source of liability is a cooling tower. Cooling towers sit on rooftops and expel heat from air conditioning systems. They produce a fine mist that can drift into nearby air intakes. If that mist carries Legionella, dozens of people can breathe it in within a matter of days. In many lawsuits, the property owner argues that the cooling tower was maintained by an outside contractor. But that argument usually fails. Hiring a contractor does not erase your duty. You are still responsible for ensuring that the contractor does the job properly. You cannot just sign a contract and walk away. You need to require paperwork, test results, and a clear maintenance schedule. If the contractor cuts corners and people get sick, you share the blame.
Hotels are another frequent target. A traveler checks in, takes a shower, and inhales contaminated mist. A few days later, they are hospitalized with severe respiratory failure. If the hotel’s hot water system has not been flushed in months, or if the water heater is set too low to kill bacteria, the hotel is on the hook. The same logic applies to nursing homes, hospitals, gyms, and public pools. Any building that supplies water to the public carries a legal burden. The larger and more complex the water system, the higher the duty. A single-family home does not face the same level of scrutiny because the occupants control the system themselves. But a commercial property or a multi-unit residential building has a landlord who holds the keys to the boiler room. That landlord holds the liability as well.
There is also a claim that does not rely on proving negligence. Some states allow a claim called strict liability for defective conditions in a building. But those cases are limited and fact-specific. In most Legionnaires’ lawsuits, negligence is the main road. That road gets wider if you ignore public health warnings, fail to register your cooling tower with local authorities, or do not follow industry standards published by organizations like ASHRAE. Regulators are not your enemies. They are your early warning system. When you skip required inspections, you hand a plaintiff’s lawyer a checklist of your failures.
What should a property owner do to avoid this disaster? The answer is straightforward. Install a water management plan. Identify all points in your system where Legionella could grow. Test those points regularly. Keep temperature logs. Flush unused lines. Clean and disinfect cooling towers on a schedule. And document every single step. If a lawsuit ever comes, your best defense is a paper trail showing you acted responsibly. The absence of that paper trail is not just an inconvenience. It is proof that you did nothing.
Legionnaires’ disease is entirely preventable. It is not a mystery illness that strikes without cause. It is a result of water systems that are ignored, underfunded, or poorly maintained. When a jury hears that a property owner spent more on lobby decorations than on water treatment, they do not feel sympathetic. They feel angry. If you own or manage a building, you need to understand that your legal duty is not abstract. It is in every pipe, every valve, and every drop of water that comes out of your fixtures. Fail that duty, and you will pay medical bills, lost wages, pain and suffering, and possibly punitive damages. The law gives you no free pass for ignorance. It does, however, give you a clear path to safety. Take it before someone gets sick.
