Fundamentals of Legionella safety in building water systems

The International Code Council (ICC) was established in 1994 as a non-profit organization dedicated to developing a single set of comprehensive and coordinated national Since the late 1970s, when I first began my career in plumbing design, Legionnaires Disease has been a hot topic because the first known outbreak that occurred during that time. I have followed the Legionnaires Disease issue and I have studied the issue and I have learned how to minimize the chance of growing Legionella bacteria in building water systems. I have served on the ASSE Legionnaires Disease Research committee for many years and I have given seminars on how to design plumbing systems to minimize the growth of Legionella bacteria, which can lead to Legionnaires Disease if aerosolized contaminated water is breathed in. I have investigated many Legionella outbreaks at hospitals, nursing homes, industrial complexes, cruise ships, hotels and in residential projects.

I have seen the pain and suffering of families dealing with death and crippling ailments caused by the disease. Because of this, several years ago, I developed a website dedicated to designing plumbing systems to minimize the growth of Legionella bacteria. The website address is I have always has an interest in this issue, and I follow what is happening with Legionnaires Disease outbreaks around the world.

Every day there are news reports about Legionella outbreaks around the world. For several years, I have used a Google application to notify me any time the words “Legionella,” or “Legionnaires Disease” are in the news or on the internet. These notifications average about three per day from various internet news sources around the world. I’m sure there are many, many more that are undiagnosed, misdiagnosed as pneumonia, or just not reported.

ASHRAE works on a Legionella standard

There has been a guideline for Legionella prevention in building water systems published by ASHRAE since 2000. ASHRAE has been working on updating the guideline and they have been working on a standard that can be adopted by building codes as a mandatory requirement for dealing with Legionella bacteria in building water systems that can lead to Legionellosis. The standard has been in development for many years and it seems like the reason the standard is taking so long to develop is there are a lot of political forces trying to delay or influence the wording in the standard. The voting committee has representation from various government agencies, water treatment consultants, cooling tower manufacturers, and laboratories, but there is no official representative for the American Society of Plumbing Engineers (ASPE) or any other plumbing related organization. (Note: ASPE's executive director has attended meetings and has participated on calls and will be considered for voting membership by the committee at the upcoming meeting in July in Seattle.)

I have been attending meetings as a non-voting member. IAPMO has had Pete Demarco attending as a non-voting member, and PVI Water Heaters has had Frank Murphy attending as a non-voting member. There are no voting members from the plumbing industry and a significant percentage of Legionellosis cases are related to Legionella growth in improperly designed or maintained domestic water systems aerosolizing contaminated water in showers and other plumbing fixtures or fittings.

ASHE asks for exemption of safety requirements

There has been a recent request made by the American Society of Hospital Engineers (ASHE) to have hospitals and health care facilities exempt from the ASHRAE Standard 188(P), which is proposed as a minimum standard to deal with the safety requirements for minimization of Legionella bacteria growth in building water systems. Their argument for being exempt was it would cost a lot of money to implement and they are required to have an infection control person in each hospital. My experience with infection control personnel, in hospitals that I have investigated, did not show they had any training on how to prevent Legionella. It seems they were mostly dealing with hand washing and sanitation of equipment to prevent the spread of infection.

The ASHE representative gave an example of how much it costs to maintain hospital doors, door closers, and door hinges, relating it to how it would also cost a lot of money to maintain building water systems to minimize Legionella. So, their opening argument seems to indicate money is more important than health and safety. I wonder if the families of Legionellosis victims who have been severely incapacitated, or died, would their attorneys agree with that logic? Their representative also said hospitals have infection control personnel that should be able to address Legionella concerns so they do not need a standard.

My response to that is, “well then, why are there so many outbreaks in hospitals?”

The reason is because hospitals are full of people who have weakened immune systems and they are more susceptible to Legionnaires Disease. I have designed plumbing systems for dozens of hospitals, and in several cases the infection control person I dealt with would not know the difference between a temperature gauge and a pressure gauge. And, they surely would not know about backflow preventers, or where they are needed and none of them knew what a balancing valve looked like or how it works. Most of them were aware of the temperatures required to prevent Legionella bacteria growth and in the same breath they would say, “but we can’t keep our water systems that hot because we will scald people,”

Ding, Ding, Ding, Ding. This is when the bells go off in my head when someone says that. When I hear that, I know they do not know how plumbing systems are designed and they do not understand how they can be designed to simultaneously keep hot water temperatures above the Legionella growth range and prevent scalding at the same time. Most of them do not realize that shower valves that meet the codes have a limit stop that is adjustable to limit the hot water temperature coming from the shower. If they knew this, they could raise the hot water temperatures above the Legionella growth range temperatures and set the limit stops to prevent scalding. This would eliminate the environment in which the bacteria grows and multiplies. At hand washing sinks in public buildings and at other fixtures where scalding is a concern, thermostatic mixing valves conforming to ASSE 1070 or an equivalent standard as listed in the code can be used to limit the hot water temperature to 120° F or less to prevent scalding. The hot water supplied to these valves should be above the Legionella growth temperature range.

Hospitals are very complex buildings, and in my experience there have been hospitals that do not have adequately trained engineering, maintenance or infection control staff. Many major hospitals do, but many more of the smaller hospitals do not have adequately trained personnel. If ASHE wants us to trust the hospitals and let them be exempt from this standard and police themselves, I say, “Show me your plan.”

If there was ever a building type in need of compliance to the ASHRAE standard, it is hospitals that are full of people with suppressed immune systems who are more susceptible to Legionnaires Disease. I have not seen any Legionella prevention plan proposed by ASHE, and until they produce a plan that meets or exceeds the minimum requirements proposed in the ASHRAE standard I hope the voting members of the ASHRAE committee do not let hospitals and/or health care facilities be exempt from the proposed ASHRAE 188 standard.

History of Legionella and how the disease got its name

Legionnaires Disease acquired its name in 1976 when an outbreak of pneumonia occurred among hundreds of people attending a convention of the American Legion in Philadelphia. A year later, when the bacterium causing the illness was finally confirmed it was an unknown pathogen and it was named Legionella Pneumophilia or Legionnaires Disease as a tribute to the American Legion members who lost their lives in the outbreak of 1976. Pneumophilia is a medical term meaning lung loving. Legionnaires Disease usually results in pneumonia or fluid in the lungs.

It has been reported that each year up to 18,000 people in the U.S. get Legionnaires Disease. Many healthy people can be infected with the Legionella bacterium and have mild flu-like symptoms, or no illness signs or symptoms at all if their immune system is strong and fights off the bacteria.

Large outbreaks of Legionnaires Disease receive significant media attention. However, this disease usually occurs as a single, isolated case in most of the cases and is not reported as an outbreak. Often, in hospitals and health care facilities people will die from pneumonia and there is never a test for Legionnaires Disease. Many cases where someone gets sick or dies from pneumonia are actually related to Legionnaires Disease. But, tests are not done to determine the cause of the pneumonia.
When Legionnaires Disease outbreaks occur, they are usually recognized in the summer and early fall when water temperatures are generally warmer. But, cases may occur year-round if water temperatures are maintained in the ideal growth temperature range. Stagnant water in schools, sports stadiums, and winter resorts, which is left unused in the piping system over a summer or long period of time, can grow bacteria to very high levels. This increases the risk when someone first uses these systems and they have a suppressed immune system. A significant percentage of people who get Legionnaires Disease and have a suppressed immune system die without quick aggressive medical treatment. Many more are severely disabled from complications related to the effects of the disease.


Legionnaires Disease can have symptoms like many other forms of pneumonia, so it can be hard to diagnose at first. The symptoms of Legionnaires Disease usually appear within two to 14 days of exposure. Symptoms include a fever, chills, and a dry or phlegmy cough. Some patients also have shortness of breath (pneumonia), muscle aches, headache, tiredness, loss of appetite, and, occasionally, diarrhea. Laboratory tests may show that these patient’s kidneys are not functioning properly. Chest X-rays often show pneumonia. It is difficult to distinguish Legionnaires Disease from other types of pneumonia by symptoms alone; other tests are required for diagnosis.


Diagnosis of Legionnaires Disease requires special tests that are not routinely performed on people with fever or pneumonia. Therefore, a physician must consider the possibility of Legionnaires Disease for them to order the right tests. Several types of tests are available. The most useful tests detect the bacteria in sputum, find Legionella antigens in urine samples, or compare antibody levels to Legionella in two blood samples obtained three to six weeks apart.

Who is at risk to get the illness?

People of any age may get Legionnaires Disease, but the illness most severely affects people with suppressed immune systems. Typically, Legionnaires Disease patients are middle-aged and older persons, particularly those who smoke cigarettes or have chronic lung disease. Also at increased risk are persons whose immune system is suppressed by diseases such as cancer, kidney failure requiring dialysis, diabetes or Acquired Immune Deficiency (AIDS). Those who take drugs that suppress the immune system (organ transplant anti-rejection drugs) are also at higher risk. Pontiac fever most commonly occurs in persons who are otherwise healthy.

Treatment for Legionnaires Disease

Erythromycin is the antibiotic currently recommended for treating persons with Legionnaires' disease. In severe cases, a second drug, Rifampin, may be used in addition. Other drugs are available for patients unable to tolerate Erythromycin.

How Legionella bacterium is spread

Outbreaks of Legionellosis have occurred after persons have breathed mists that come from a water source (e.g., showers, air conditioning cooling towers, whirlpool spas, or any other aerosolized water source that is contaminated with Legionella bacteria.) People may be exposed to these mists in homes, workplaces, hospitals, or public places. Legionella bacteria is not limited to a building type or size. If the conditions are right for the bacteria to grow and it is present in the water supply, then it will grow in numbers. Legionella bacteria is not passed from person to person.

Where the Legionella bacterium is found

Legionella organisms can be found in many types of water systems. However, the bacterium reproduces in high numbers in warm, stagnant water, such as that found in certain plumbing systems and hot water tanks, cooling towers and evaporative condensers of large air-conditioning systems, and whirlpool spas. Cases of Legionnaire’s Disease have been identified throughout the U.S. and in several foreign countries. Legionella bacteria grows worldwide wherever the ideal conditions for the bacteria growth are present.

Prevention of Legionnaires Disease in plumbing. HVAC systems

Improved design and maintenance of cooling towers and plumbing systems to limit the growth and spread of Legionella organisms through contaminated water vapor transmission are important for Legionnaires Disease prevention. However, in my opinion, it is far more important to prevent the conditions where the bacteria will grow than to try to redesign products to minimize the transmission of water vapor.

According to many sources, Legionella bacteria is common in water supplies. The bacterium thrives when it is exposed to the proper environment for growth. Warm or hot stagnant water, between 68 °F and 122 °F, provides an environment for bacteria growth.

Emergency disinfecting methods

There are two common emergency disinfection methods and five common continuous disinfecting methods to kill the Legionella bacteria. Building owners should use one of the following treatment methods to treat piping systems containing hot water storage tanks, cooling towers and hot tubs using one or more of the following methods. It should be noted that it is not easy or safe to thermally or chemically disinfect domestic hot water systems without posing a scald or health hazard to humans than may use or consume the water.

Heat and flush method

The heat and flush method involves heating the system to at least 151°F and then circulating the water through the system. This raises the potential for scalding and should be done only in controlled conditions.

Hyper-chlorination method

The chlorination method is where high concentrations of chlorine are introduced to the hot water tank and then the hyper-chlorinated water is circulated through the system and flushed until it reaches each outlet. The high concentrations of chlorine must be maintained for a couple of hours. Hyper-chlorination can be unsafe in drinking water systems and cautions should be employed to do this in a controlled environment.

Continuous disinfection methods

The Temperature Maintenance method involves maintaining the hot water system distribution supply and return temperatures above 124°F, which is a couple of degrees above the growth temperature range and then circulating the water through the system. This raises the potential for scalding and should be done only in controlled conditions.

The Ultraviolet Radiation method employs using a Ultra-Violet (UV) Radiation Unit to kill Legionella bacterium before it enters the building water distribution system.

The Ozonation method is where an ozone generator produces ozone for injection into the water system. Ozone is dissolved into the water to achieve a dose of about 1 to 2 milligrams per liter. The Ozone kills the Legionella bacterium. Ozone generators can have an expensive first cost.

The most practical way to prevent Legionella bacteria in domestic hot water systems is to use the copper-silver ionization method. Copper-silver ionization has been found to kill Legionella bacterium without causing harm to humans.


Periodic flushing of all branch piping brings in fresh chlorinated water from the public water supply. Chlorine, monochlorine, or some other form of water treatment chemical, is typically added to all public water supplies in the U.S. Chlorine dissipates over time and within a few days may be ineffective at fighting Legionella bacteria. So, if your building has stagnant branch piping that can go for days or weeks without flowing, it may be a good idea to consider having an automatic flushing valve on each branch that may sit idle for long periods of time.

Recently, I became aware of a company in Germany that has new pipe fitting called a flow splitter fitting that would work well in this application. Utilizing a flow splitter fitting to eliminate all dead legs in the piping system would require some additional piping on branches. But, it allows the design to utilize a commonly used fixture such as a water closet, dishwasher or laundry machine to be at the end of a plumbing system which allows for flushing of all the branches between the source and the commonly used fixture.

In cases where the entire building is idle for a long period of time, using a motorized valve to periodically flush the system is advisable. This periodic flushing can be done on a time clock to empty the contents of the system, or using the temperature sensor which measures the ground water temperature where it flushes the ambient temperature water from the building and brings in chlorinated water to minimize the conditions which can contribute to bacterial growth.

Ron George is president of Plumb-Tech Design and Consulting Services LLC. He has served as chairman of the International Residential Plumbing & Mechanical Code Committee. Visit, e-mail or phone (734) 755-1908.

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