Air Conditioning Condensate Recovery

by | Jan 15, 2013

Air conditioning and refrigeration are used around the world for temperature comfort and food preservation.  As the air is being cooled, it is dehumidified, causing water to be removed as condensate.  With proper treatment to address biological contaminants, this water can be constructively used.

A typical air conditioning system in a commercial building consists of an air-handling unit that circulates air to the occupied spaces to maintain comfort.  As the air returns from the space, it is mixed with outside air, which is necessary to maintain a healthful environment.  As the air passes through the air-handling unit, it goes through a cooling coil.  The temperature of the air drops, and the humidity, from the added outside air and moisture from the space, is removed as condensate.

Condensate is essentially distilled water, low in mineral content, but may contain bacteria.   Air conditioning condensate can amplify Legionella and other airborne bacteria, and it has been shown to be the source of outbreaks in hospitals, motels, and cruise ships.  Contamination of air conditioning condensate by Legionella is so common that there are commercially available kits for inhibiting microbial growth in the condensate.  High levels of Legionella are cause for concern.  Most natural sources of water are not contaminated, but can become problematic when an amplifying device, such as an air conditioner, is present.

Untreated condensate should be handled in a manner to eliminate any possibility of creating aerosols that can be inhaled by humans.  Condensate reuse may include subsurface irrigation or process makeup (such as a cooling tower), where water is treated for biological contamination.

If it is to be used for potable water or for washing, proper disinfection of the water is required.  Ultraviolet light, chlorine tablets, ozone injection, and/or raising water temperature to at least 140 degrees Fahrenheit reduce the potential hazard of biological contamination.  Reclaimed air conditioning condensate is high-quality water with low mineral and chemical content and has many potential uses, but care must be taken with its use.  Distribution in a fashion that would cause aerosols (e.g., lawn sprinklers) should be avoided due to the possibility of person in the vicinity being exposed to Legionella bacteria.  If the use of air conditioning condensate could expose persons to inhalation of bacteria, then purification of the water should be done prior to use.


Examples of common applications are as follows:

  • Landscape irrigation (no treatment needed if utilized for subsurface irrigation)
  • Swimming pool (with biocide treatment)
  • Domestic water (with biocide treatment)
  • Cooling tower makeup (can  likely run direct to tower without modulating valves)
  • Industrial process makeup

Hybrid systems are being developed that route the condensate into the rainwater catchment cistern.  The rainwater needs to be considered as part of a gray water system.  This means that if used for lawn irrigation, it should be used with subsurface irrigation systems.   Aerosols are a possible from flushing toilets, therefore if the water is brought into the building for flushing toilets, it needs to be filtered and sanitized before use.

Condensate from air conditioning units is an often overlooked source of freshwater.  The resultant accumulation (which can be just a trickle or sometimes more) can provide a sizable amount of freshwater that can be constructively used to offset the use of potable water. The low mineral content in condensate causes less fouling from mineral residue in the evaporation process thereby making water ideally suited for use in cooling towers and fountains.  The single caution for condensate reclaim use would be that aerosols may be created in an occupied space.  In this case, treatment for biological elements contained in the water would be appropriate.

As water shortages become more widespread, condensate from air conditioning is gaining increased attention for creative non-potable and potable applications.  If the potential hazard of bacteria from aerosols is addressed, the designer of an air conditioning condensate collection system can utilize this source of water as a viable supplement.

Bob Boulware is President of Design-Aire Engineering, Inc. Bob is a past president of the American Rainwater Catchment Systems Association (ARCSA) and an Accredited Rainwater Systems Design Professional. He is a 30+-year member of ASHRAE and past president of the Central Indiana Chapter of American Society of Plumbing Engineers (ASPE) and serves on the ASPE National Standards Committee. Mr. Boulware is a member of the International Association of Plumbing and Mechanical Officials (IAPMO) Alternative Water Sources Committee, and helped to develop the Green Plumbing Supplement to the upcoming editions of the Uniform and the International Plumbing Codes.  Mr. Boulware has taught Environmental Design for mechanical and electrical systems at Ball State University and plumbing design at IUPUI.  Follow us @daengineering on Twitter &   Bob can be reached at

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