Multi-Dwelling Homes


Multi-Dwelling homes include condominiums, apartments, townhouses and duplexes. These building’s plumbing pipes may be at higher risk for Legionella than single family homes due to the possibility of having larger, more intricate water systems. The control of these systems frequently are the responsibility of the landlord or facility operator, but some cleaning can be maintained by the tenant. In these circumstances, it is the facility operator’s responsibility to ensure proper maintenance and water temperature, whereas, it is the responsibility of the tenant to maintain regular cleaning of showerheads, faucets and personal humidifiers within their apartment or condo. Tenants can follow the instructions outlined for Homeowners for routine maintenance of showerheads, faucets, and humidifiers. Multi-dwelling facilities differ from single family homes in that they may have the following features that can increase the risk of bacterial growth and transmission:

  1. Hot tubs/ Jacuzzis / spas
  2. Pools and shower facilities
  3. Indoor or outdoor fountains or water features
  4. Central water heaters and distributed water lines/pipes
  5. Cooling towers
  6. Water reservoir tanks
  7. Humidifiers
  8. Solar water systems
Therefore, facility mangers of these buildings should have standard operating procedures for the routine maintenance and sanitation of these features. Some general guidelines are provided below:

Hot Tubs/Jacuzzis and Spas

Hot tubs/Jacuzzi and spas should be periodically inspected by health officials to ensure they are properly operating and appropriately cleaned. Facility Managers should check the disinfectant residual and pH twice a day and have a standard schedule for regular cleaning, making sure to scrub biofilms or algae from the sides of the tub. Unit filters should be replaced in accordance with the manufacturer’s specifications. If Legionella is detected in hot tubs, Jacuzzis or spas, then operators should follow  CDC or ASHRAE guidelines for cleaning and disinfecting them.


Much of the same guidance for hot tubs also pertains to pools. The CDC outlines guidance for pool operators including a 12-step program for prevention of recreational water illnesses, training, procedures for pool operations, and videos and guidance for the safety handling of pool chemicals. Facility operators should be knowledgeable and compliant with all applicable laws and regulations. Shower facilities associated with pools should have the shower heads cleaned and disinfected on a quarterly or regular basis.

Water Fountains/Features

Decorative fountains and other water features (e.g., ponds, bubblers, bird baths, etc.) particularly those indoors can be a source of risk for Legionella growth and transmission. Facilities with these features should have a written operating procedure for cleaning and disinfection to minimize potential growth of Legionella (and other waterborne microbes) and maintain proper records of treatment and maintenance.

Hot Water Heaters

Multi-dwelling facilities may use a variety of hot water systems, so it is not possible to generalize on operational and maintenance guidelines.  Where units have individual hot water heaters, the guidelines recommended for Homeowners can be used. Legionella can multiply in plumbing systems when water temperatures are between 20-45°C (77 to 108 oF). The bacteria are not active below 20°C and do not survive above 60°C. Keeping the water heater at the proper temperatures can significantly decrease the likelihood of Legionella growth the plumbing system. Hot water heaters should store water at least 140°F and distributed at 122°F or higher, but to minimize the risk of scalding, thermostatic mixer valves need to be fitter as close to possible to outlets. 

Facilities with a central hot water heater and distributed piping to deliver heated water to individual units should follow the recommendations outlined in the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standard for building water systems (ANSI/ASHRAE Standard 188-2015).


Cooling Towers

Large multi-dwelling buildings may have a central cooling system that uses cooling towers or evaporative cooling systems. Procedures for operating and maintaining these systems are addressed in the ASHRAE standard for building water systems (ANSI/ASHRAE Standard 188-2015). These buildings should have a building water safety plan, as defined in ASHRAE 188, and follow it closely as numerous Legionella outbreaks have been associated with poor maintenance of cooling systems.

Water Reservoir Tanks and Cold water systems

Procedures for the operation and maintenance of water reservoirs and cold water systems are addressed in the ASHRAE standard for building water systems (ANSI/ASHRAE Standard 188-2015). Particular care should be taken for rooftop storage tanks to ensure that they are properly screened and vented to protect against entry of birds or insects. An annual check of these systems is recommended.