Systems should be treated with corrosion and scale inhibiting chemicals, periodically cleaned and sanitized, and equipped with proper chemical feed and monitoring systems from first start-up.

Some corrosion processes, such as microbiological corrosion caused by specific organisms called sulfate reducing bacteria, can cause holes in piping in periods as short as a year and, once established, are difficult or impossible to remove from the system.

Corrosion is a Particular Problem in New York

New York City water contains relatively small amounts of dissolved minerals. Such supplies are commonly called "soft waters." This type of water is preferred to "hard water" because it is less likely to cause problems associated with mineral deposition or scale in piping, heating systems and air conditioning equipment. Unfortunately soft waters can be quite aggressive to piping.

The corrosion of iron piping produces various forms of iron oxide (magnetite, hematite, etc.,). The local environment (oxygen rich or poor, degree of microbiological activity) determines the types formed. In all cases, these corrosion products are more voluminous than the metal loss that produces them. In some instances, they may be as much as 10 or 20 times as voluminous. When iron piping is used to supply open spray condenser water to package air conditioning units, the piping often experiences fouling with corrosion products causing downtime and premature failure of the system.

Microbiological Issues in Cooling Towers

Condenser water systems are easy breeding grounds for algae, bacterial slimes, fungal growths and other organisms that can cause such severe fouling that the system cannot function.  Additionally, cooling towers have been associated with the amplification and transmission of disease causing organisms such as the bacteria that cause Legionnaire’s Disease.

Legionnaire's Disease is an acute pneumonia type respiratory infection caused by a bacterial organism.  Without treatment up to 15% of the cases can be fatal, but with effective antibiotic treatments now available more than 96% survive.  The organism appears to be present in many fresh water systems and may be carried through the air in water aerosols.  This bacteria has been found in from air conditioning towers, in ponds, fresh water supplies, shower heads, etc.

The disease was first identified following a dramatic outbreak that occurred at a Philadelphia hotel during an American Legion convention.  This outbreak turned out not to be an isolated incident.  There have been other outbreaks at hospitals, office buildings, and at other hotels.  In 1985, 27 people became ill and 3 died after staying at the Hilton Airport Inn in Romulus, Michigan.  Each year in New York City, many suspected or confirmed cases of Legionnaire's Disease are reported to health officials.

The New York City Department of Public Health Engineering issued guidelines in 1980 regarding the cleaning, disinfection and waterside maintenance of Cooling Towers and Condenser water systems.  These Cooling Tower Guidelines remain in effect and we provide them here.

Water in many natural or man-made systems may serve as amplifiers of Legionella by providing suitable conditions for growth.  These include cooling towers, evaporative condensers, humidifiers, potable water heaters, holding tanks, shower heads, faucet aerators, etc.  Legionella apparently can survive in low numbers in routine water treatment used to produce potable water and may be carried into cooling towers through the make-up water or scrubbed from the air.  Many health authorities discourage the notion of completely eliminating Legionella from environmental waters except for areas occupied for immuno-compromised individuals or for water used for therapeutic purposes.

All cooling towers should be cleaned and disinfected with alkaline detergent chemicals and compatible biocides at least once each year and sanitized at least twice annually for systems operating year round.