Many people assume a brand-new home has pristine water quality, but experts warn that newly constructed homes — particularly those in multifamily apartment complexes with large cooling systems — can develop Legionella bacteria contamination if water sits stagnant in pipes during construction delays or before occupancy, or if systems aren’t properly maintained.
The bacteria have also been found in unexpected places ranging from vacation rentals or spare bathrooms that go unused for days to hot tubs, CPAP machines and room humidifiers.
Legionella is found naturally in lakes, ponds, streams and other freshwater settings, but it can become dangerous when it grows and spreads in a home or building’s water systems and plumbing — or wherever there is stagnant water. Inhaling the bacteria through tiny water droplets can lead to Legionnaires’ disease, a serious type of pneumonia, or Pontiac fever, a less-serious upper respiratory form of the illness.
“Shower heads, sink faucets and humidifiers can create spray, or small droplets, that can release bacteria into the air,” writes the Environmental Protection Agency in an indoor air quality alert. People can become infected when they breathe in spray or small droplets containing Legionella, it said.
Legionnaires’ disease is a pneumonia that causes flu-like symptoms in most people but can be more dangerous — even fatal — for people who have known risk factors for severe disease including smoking, chronic conditions, a compromised immune system, or being older than age 50.
In 2015, the U.S. experienced two of the deadliest Legionnaires’ outbreaks in history. In the South Bronx, 138 people were sickened and 16 died; the outbreak was traced to a cooling tower on the roof of an apartment building. In Flint, Michigan, at least 87 people became ill and 16 died from bacteria found in the city’s drinking water.
More recently, in 2025, an outbreak of Legionnaires’ disease in Harlem sickened 114 people and killed at least seven, according to the New York City Health Department. The outbreak was ultimately traced to a cooling tower at Harlem Hospital and contamination of a nearby construction site on West 137th Street.
The cluster reemerged in Harlem in winter 2026 when several residents of large apartment buildings became sick. City health officials traced the outbreak to the buildings’ hot water systems.
The CDC investigated the sources of Legionnaires’ outbreaks between 2000 and 2014. A little over one-third of cases (35%) came from so-called “external changes.” Within this category, there were two major risk factors: Natural disasters accounted for a quarter of those sources, while construction work accounted for the remaining three-quarters.
“That’s a huge figure, and one that points to the importance of focusing on legionella as a real risk when planning construction projects of any size or kind,” write the biologists from Legionella Control, an international organization that studies the bacteria’s risks. “We may not always be able to predict and prevent legionella risks stemming from unexpected natural disasters, but we can certainly do a lot to prevent the legionella risks associated with building works.”
Post-COVID Urgency and Empty Homes
The National Association of Realtors warned real estate agents and property managers about the risks of Legionella after prolonged closures of buildings, homes and construction jobs during the pandemic. The same principle applies to vacation properties that are closed up for weeks at a time.
The Centers for Disease Control and Prevention issued guidance for reopening buildings after prolonged shutdowns advising that building and homeowners:
- Develop a comprehensive water management program for all water systems and devices
- Ensure water heaters are properly maintained and temperatures are correctly set
- Flush water systems
- Clean any decorative water features
- Ensure hot tubs/spas are safe
- Ensure cooling towers are well-maintained and clean
- Ensure any safety equipment such as sprinkler systems are well-maintained and clean
- Maintain water systems
And, Purdue University’s Center for Plumbing Safety also studied water safety in buildings that were shut down and made recommendations for avoiding bacteria growth, pipe leaching and other issues associated with low or no regular use.
Hotels, Vacation Rentals and Hot Tubs
The CDC also warns that vacation rentals and hotels with systems that aren’t properly maintained can be at risk of the disease. Vacation homes, in particular, where water may sit stagnant during the off-season, pose a higher risk, the CDC says.
Nearly 1 in 7 Legionnaires’ disease patients reported staying overnight at hotels, private homes or vacation rental properties, the CDC says, with about half of those reporting they’d used a hot tub.
Other types of buildings that can experience long-term periods of low or no use include schools over the summer, ski resorts, snowbird communities, buildings unoccupied between owners, and seasonal or vacation homes.
Official Warnings and Guidance
The Occupational Safety and Health Administration (OSHA) explicitly warns that new water systems require thorough cleaning and disinfection, as construction material residue and stagnant water promote accelerated Legionella growth.
Water hygiene experts note that many newly built properties do not undergo robust water system commissioning before handover. Experts advise that all new plumbing should be thoroughly flushed, tested and assessed for risk before regular occupation.
Both the EPA and the CDC advise residents moving into new or vacant homes to run their cold and hot water faucets on low before initial use to purge stagnant water that has lost its disinfectant residual.
The New York State Health Department recommends the following to protect yourself in and around your home:
- Flush Your Plumbing: If a new home has been sitting empty, let both hot and cold faucets run for at least three minutes. Avoid standing directly over or splashing the water while flushing to avoid inhaling any potential aerosolized mist.
- Set the Temperature High: Check your water heater. Setting the thermostat to 140°F is often hot enough to kill Legionella throughout the plumbing.
- Drain garden hoses and avoid leaving water-filled hoses lying in the sun. Warm, stagnant water promotes the growth of Legionella and other bacteria.
- Medical Equipment: Use the type of water recommended by your in-home medical equipment or healthcare provider. This includes humidifiers, CPAP or BiPAP machines, and neutralizers. Follow the manufacturer’s instructions for cleaning and use. Follow the advice from your healthcare provider if they recommend using sterile water.
- Clean Filters: Follow the manufacturer’s instructions for cleaning and replacing all water filters, including whole-house water filters, and point-of-use filters (tap or refrigerator water/ice maker).
- Maintain Hot Tubs and Pools: Regularly check the chlorine level in your pool or hot tub; chlorine can kill Legionella and other bacteria.
- Avoid if Possible: People who are at higher risk should avoid using devices that recirculate water, such as decorative fountains, where Legionella can grow.
- Raise Your Water Temp: Consider raising your hot water heater temperature to between 130°-140° F. Hotter water kills Legionella but also increases the risk of hot water burns. You can also mix hot and cold water at the tap before use to avoid injury.
- Flush Hot Water Heaters: Flush your hot water heater twice a year and follow the manufacturer’s recommendations for maintenance.
- Consider a Water Softener: If you have hard water, a water softener will stop the buildup of scale in your piping that can provide a breeding ground for Legionella.
Top image: TrueCreatives, via Canva.com
