CHICAGO — Much has been written about how to minimize the risk ofLegionellain cooling towers, but how do you minimize the risk of the potentially deadly bacteria in building water systems, such as hotel spas and drinking water?

A forum at the American Society of Heating, Refrigerating and Air-Conditioning Engineers Inc. (ASHRAE) Winter Meeting examined the topic, along with the use of “Guideline 12-2000: Minimizing the Risk of Legionellosis Associated with Building Water Systems.” The Technical Committee for Water Treatment wanted to know how people are using the guideline — or whether they are using it at all.

The guideline, according to the committee, is an easily digestible 12 pages. It contains information on drinking fountains and spas, optimum temperatures at which water can kill the bacteria, and service and maintenance procedures.

It is intended for use by maintenance personnel, designers, owners, and end users.

The Discussion Starts

A consulting engineer commented that over a period of five to six years, he ran into several cases of legionellosis. “Most that we find come from a cooling tower,” he said. In one particularly big case,Legionellawas discovered in the cooling tower, but the strain in the cooling tower didn’t kill people. The deadly strain was in the domestic tempered water.

“The Centers for Disease Control (CDC) doesn’t even investigate until two people die,” he said. “Do we want to live that way?”

Another consulting engineer stated that when he recommends that the customer follow the ASHRAE guidelines, he feels that he has headed off potential litigation.

An engineer remarked that even customers who test their systems for Legionella are not necessarily safe, because they may only test once and feel that they are safe. It is a false sense of security because “Single tests may not find Legionella.” Regular testing is needed.

Another engineer pointed out that symptoms of Legionnaire’s disease are so close to pneumonia, many people are misdiagnosed. “If antibiotics don’t work in the first day or two, have them tested for legionellosis.”

The bacteria thrives in temperatures between 77 degrees to 108 degrees F; this includes the temperature range in which whirlpools operate. Water treatment programs for these systems may require oxidizing biocides.

Why Use It?

Why use the document? Because “It’s an excellent piece of work,” responded an audience participant. It can also be applied to water control/treatment for healthcare facilities, where immune-compromised individuals are at risk from infectious agents.

Cooling tower manufacturers’ salespeople should be carrying the document with them, pointed out an audience member, “but we know they’re not.” The guideline is available free at some manufacturers’ Web sites.

One operating engineer confessed that he didn’t know about the guidelines; he was attending this forum because of his professional interest in Legionella. He also was curious about testing procedures.

An even smaller document is possible for the care and maintenance of cooling towers, a committee member said.


A heating system manufacturer said that he hasn’t seen the guideline specified. Then he asked whether using hot water heat to temper building water systems is sufficient.

It depends on the temperature, was the reply. Fear of scalding is valid, but water needs to be at least 140 degrees for bacteria to be killed; 160 degrees is safer still.

Even when water is tempered to 140 degrees and higher, a dead leg can be an area of bacterial growth, an engineer pointed out. Once bacteria is found, recurrence of its growth is high unless different steps are taken to treat the water system.

In Singapore, every cooling tower is assigned a number, said a consulting engineer, and the government inspects them. No Legionella has been reported thus far; however, there has been no testing of atypical pneumonia either, so some cases might be misdiagnosed.

Residential hot tubs are also a critical area of concern because so many owners don’t want to use chemical treatments, an audience member commented. “We have to make sure people understand.” Residential hot tubs are not covered in the guideline, but there is enough knowledge to cross over, he said.

Healthcare facilities are at the greatest risk, it was concluded, because of the higher proportion of immune-compromised inhabitants. In the general public, 5 percent of all people are immune-compromised, an engineer stated. “You might be a healthy 35 year old now, but in 20 to 30 years that could change.”

Publication date: 03/24/2003