According to the Centers for Disease Control and Prevention (CDC), during the period between 2000 and 2018, the rate of reported cases of Legionellosis increased 900% in the United States, with thousands of cases reported to the CDC each year. According to the CDC, approximately 9% of reported Legionellosis cases are fatal. Data from recent years show this trend for increases continuing upward. It is more likely than not that this upward trend in reported cases of Legionellosis — which includes both Legionnaires’ disease and Pontiac fever (a milder, influenza-like illness in the Legionellosis family) — is associated with several factors, including water and energy conservation efforts over approximately the same time period.
Over the same period in which the CDC has documented a significant increase in reported cases of Legionellosis, we have seen reductions in flows associated with water conservation programs, starting with the Energy Policy Act of 1992. In recent years, we have faced further challenges of reduced water flows in the name of many voluntary water conservation programs on top of the Energy Policy Act reductions. These conservation programs are causing significantly lower flows and aging water, which promotes Legionella bacteria growth. Efforts to save energy and water have had the unintended consequences of causing microbial growth in piping systems, due to aging water.
As energy and water conservation measures were implemented, lower water flows in buildings caused lower water flows in utility mains, allowing chemicals to dissipate to levels that will not control bacterial growth. This negatively affected the quality of utility water entering buildings. The changes in water quality are associated with lower water treatment chemical residuals and higher levels of bacteria and other microorganisms at the far ends of distribution systems due to stagnant water conditions in the utility distribution system.
PRE-EXISTING INFRASTRUCTURE: THE SIZE OF WATER UTILITY MAINS
Water utility mains are generally sized to supply water to fire hydrants for purposes of fighting fires, and most cities have a minimum water main size of 8 to 12 inches. These pipe sizes are much larger than what is needed to supply potable water for household purposes, such as drinking, bathing, and washing. These pre-existing, larger pipe sizes have contributed to the stagnation and aging of water in utility mains since the implementation of the Energy Policy Act of 1992, which regulated the manufacture, sale, and installation of low-flow plumbing fixtures.
At the turn of the 20th century, there were many large fires and conflagrations where major cities were burned to the ground. There was inadequate water available to control the fires, so fire officials and insurance companies urged local governments to construct larger water mains and install fire hydrants to allow firefighters easy access to a reliable supply of water to fight fires. The water utilities established standards for the sizing, installation, performance, and testing of water mains through the American Water Works Association (AWWA). The AWWA standard included minimum sizes of water mains and minimum distances between fire hydrants, which were spaced every few hundred feet. Most jurisdictions have adopted the AWWA standards. When indoor plumbing exploded after World War II, with the development of suburbs, the large water mains were simply extended to serve the new suburbs or were actually increased in size based upon the downstream demand, which was based on the fixture flow rates that were much higher than now.
GOOD INTENTIONS: CONSERVATION OF ENERGY BY CONSERVING WATER WITH LOW FLOW RATES
The Energy Policy Act of 1992 regulated the manufacture, sale, and installation of low-flow plumbing fixtures. Residential occupancies were required to comply with low-flow fixture requirements in 1994, and commercial buildings were required to comply with low-flow fixture requirements in 1996. Prior to 1992, water closets generally flushed anywhere from 3.5 to 7 gallons per flush, and then were reduced to a maximum of 1.6 gallons per flush (79.2% reduction). Prior to 1992, showers flowed anywhere from 3 to 12 gallons per minute, and then were reduced to a maximum of 2.5 gallons per minute (77.2% reduction). Prior to 1992, lavatory and sink faucets flowed anywhere from 3 to 7 gallons per minute, and then were reduced to maximum flow of 2.0 to 2.2 gallons per minute (71.5% reduction).
Domestic water use today is less than 20% of the flows prior to the Energy Policy Act of 1992, and using today’s ultra-low-flow fixtures, flow rates show over an 80% reduction in water use.
UNINTENDED CONSEQUENCE: STAGNANT AND AGING WATER IN UTILITY MAINS
Mandatory reductions in water use at the plumbing fixtures (lower flow rates at fixtures) and further reductions in water use through voluntary water conservation programs have had the unintended consequence of lengthening the time from when water leaves the water utility to the time the water reaches the building service entrance. Today, it takes about five times as long, or longer, for water to reach the end-user in a water utility distribution system than before 1992.
The velocity of water (distance traveled over time) is dependent upon the flow rate of water through a given pipe size. Water at a given flow rate will move more slowly through a larger pipe than through a smaller pipe. When the flow rate is significantly reduced (to less than 20% of the pre-1992 rate) through the same size water main, the velocity of the water will also be reduced to 20% of the prior flow rate, thereby increasing the time it takes the water to travel a specified distance by a factor of 5. What once may have taken three to five days for water to flow from the water treatment plant to the end-user will now take 15 to 25 days.
As water flows are continually reduced, in a sort of water conservation game of limbo, or “how low can the flow go,” the flow velocities in water mains, which are sized for fire flows, are so low that water utilities were experiencing water utility flow rates around 20% of the flow rates in water mains prior to the Energy Policy Act of 1992. The low flow velocities in water mains allows the water to age in the utility mains. As a result, chemical treatment added to the water by the utility, such as chlorine, oxidizes or dissipates down to levels that are ineffective at controlling bacteria growth before the water reaches the ends of the water utility distribution systems.
RESPONSE BY WATER UTILITIES: CHANGES IN CHEMICAL TREATMENT TO COMPLY WITH THE SAFE DRINKING WATER ACT
Before 1992, the primary disinfectant in use was chlorine. Chlorine typically must be above 0.5 parts per million (ppm) of free chlorine to be effective against Legionella bacteria and other organisms in the water supply. However, chlorine can dissipate in as little as five to 10 days to levels that are ineffective at controlling Legionella bacteria in the municipal water main piping distribution system. The farther water flows out in water utility distribution systems, the more the chlorine or water treatment residual will dissipate down to a level that will no longer control Legionella bacteria growth. This aging water issue, and resultant low levels or non-existent chlorine residuals at or near the ends of the water utility distribution systems, made it difficult for water utilities to comply with the Safe Drinking Water Act of 1974, which regulates the quality of water supplied to the end-user.
The Safe Drinking Water Act, signed into law in 1974, gave the Environmental Protection Agency power to set national health standards for drinking water “to protect against both naturally occurring and man-made contaminants that may be found in drinking water.” The Act prescribed a minimum residual of free chlorine (chlorine was the chemical used by most water utilities to control bacteria growth in the water main piping at the end of the utility main line). In the years preceding 1992, in these large water mains, water from the treatment plant would reach the end of the main line in three to five days, and the testing of the water at the end of the main line would yield acceptable disinfectant residuals per Safe Drinking Water Act regulations.
Chlorine would be expected to have a measurable residual at the end of the system in the years before the Energy Policy Act of 1992. However, chlorine would not be expected to have a measurable residual that could control Legionella bacteria growth after 15-25 days. As a result, many water utilities implemented changes from their normal water treatment process.
Increased Chlorine Levels: Some water utilities increased levels of chlorine to the maximum allowable limits (increasing the parts per million or milligrams per liter of chlorine) to have a chlorine residual that is sufficient to control Legionella bacteria and other microorganism growth at the ends of their distribution systems.
Change from Chlorine to Monochloramines: Some water utilities have changed their disinfection method to monochloramines, which will allow a measurable residual at the end of the system but will not be as effective as chlorine in reducing overall Legionella bacteria count from entering the building water systems.
Monochloramines have disinfection byproducts that also serve as a food source for nontuberculous mycobacterium (NTM), a dangerous contaminant found in some water systems. When water treatment chemicals drop to levels that are insufficient to control NTM, the NTM feeds on the byproduct of monochloramines, and NTM can grow to high levels in potable water building water systems. Monochloramines are a chlorine and ammonia combination chemical and must be maintained between 4 parts per million (the EPA recommended maximum) and 1 ppm (the minimum level that is effective at controlling microbial growth in water distribution systems).
MORE UNINTENDED CONSEQUENCES: INCREASES IN LEGIONELLA BACTERIA AND OTHER MICROBES ENTER BUILDING WATER SYSTEMS
Water quality supplied by a utility can be affected by the piping material, the time of year (which affects temperature), source water quality, and biofilm growth in the water mains; all of this will affect the water treatment chemical residuals at the end of the system. In remote water utility mains, it is possible for water to have been in the utility main so long that the water treatment chemicals have dissipated down to levels that are no longer effective at killing bacteria and other micro-organisms in the water.
Corrosion: In larger or unevenly distributed systems, higher chlorine residuals and concentrations of monochloramines higher than 4 ppm increase the rate of corrosion and can have harmful effects on the piping materials, valves, and components in the utility distribution system and the building water distribution system. They also increase the number of dissolved metals in drinking water, such as lead, copper, iron, zinc, magnesium, and other filler metals of the water distribution piping system components. Monochloramines have also been known to affect rubber gaskets, O-rings, seals, and gaskets in some joints of building water systems, including plumbing systems.
DISINFECTION BYPRODUCTS: INCREASED BACTERIA IN SURGE FLOWS
In addition to low flows and chlorine dissipation, which can fall short of controlling Legionella bacteria from entering building water systems, a surge flow creates a condition that scours the biofilm off the piping wall, allowing a large dose of bacteria, like Legionella and other microorganisms, to enter the flow of water in the water main and overwhelm the normal levels of chemicals in the water. The bacteria will grow and thrive in the biofilm until there is a high-velocity flow event that dislodges or sloughs off a large amount of this biofilm. These surge flows can occur through fire events, drawing water out of a fire hydrant for other reasons, including repair and replacements on water mains, water hammer, construction activities, and water main breaks, to name a few.
RESPONSE: CHANGES IN POTABLE WATER DISINFECTION AND TREATMENT METHODS IN BUILDING WATER SYSTEMS
The measures to disinfect potable water and other building water systems have adapted, or changed, to meet the threat of contamination by Legionella bacteria and other harmful microorganisms that enter a building’s water distribution system through the municipal water supply. Efforts to control the growth of Legionella bacteria and other microorganisms often include adding secondary or supplemental water treatment chemicals inside the building, near the building water service entrance, and raising the hot water temperature above the Legionella bacteria growth temperature range. The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) has published two important documents that address control of Legionella in building water systems. ASHRAE Guideline 12, Minimizing the Risk of Legionellosis Associated with Building Water Systems, first published in 2000, and ASHRAE Standard 188, Legionellosis: Risk Management for Building Water Systems, first published in 2015, recognize the danger of Legionella bacteria in potable water distribution systems. ASHRAE Guideline 12 provides guidance useful in the implementation of ASHRAE Standard 188, whereas ASHRAE Standard 188 gives direction regarding what to do to control the spread of Legionellosis, such as implementing a water management program. ASHRAE Guideline 12 gives direction on how to do it. Both documents address the need to monitor and control the water temperature (“physical methods”) or water treatment chemical levels (“chemical methods”) to minimize Legionella bacteria growth. The documents also address emergency remediation procedures to kill or eradicate Legionella bacteria in potable water systems, and Guideline 12 provides specific guidance on the use of high temperatures and elevated chemical treatment levels.
