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Understanding ASHRAE Standard 188—Prevention of Legionellosis Associated with Building Water Systems

A new ASHRAE Standard for building water systems will soon be the measure of industry best practice and help mitigate the formation of a dangerous waterborne pathogen.
By Capt. Michael P. Doyle, P.E., LEED AP, M.SAME, USN (Ret.), and Melissa Cain

Mineral scale and microbio fouling in a high efficiency honey-comb tower fill.

Water treatment industry experts agree that failure to prevent legionellosis, or Legionnaires’ disease, is the most significant water treatment problem today. It is estimated 11 people per day die from the disease. Essentially, every case is the result of exposure to inadequately managed building water systems—problems that can be prevented.

Both utility and potable water systems can be the source of the hazard. As a result, a consensus of industry experts came together to move the current ASHRAE Legionella Guideline (12-2000) to a full ASHRAE Standard. After several years of work, Standard Project Committee 188 (which has federal government representation) completed the Standard document and released it for its first of two 45-day public reviews in October 2010. After incorporating much feedback, the Standard is now moving toward publication in the second half of 2012. Facility owners would be well served to review this Standard and determine the best path to address its new requirements.

ASHRAE Standard 188, entitled Prevention of Legionellosis Associated with Building Water Systems, is a risk management Standard that establishes absolute requirements for prevention of legionellosis tied to building water systems. A brief, but not complete, summary of building types included in the Standard are all buildings with cooling towers; all buildings with spas, or misters, dehumidifiers, air washers or decorative fountains; all buildings with centralized hot water heaters; all buildings 10 stories or taller; all healthcare facilities; and all buildings receiving water containing less than 0.5-ppm of total residual oxidant as chlorine.

Implementing a Solution
An ASHRAE Standard is neither a rule nor a regulation—but from a legal perspective, it is a “standard of practice.” Therefore, from a liability standpoint, Standard 188 applies to the owners and managers of most commercial, industrial and institutional buildings in the United States.

As was the case with ASHRAE Standard 62 for indoor air quality, the industry expects ASHRAE Standard 188 to become part of local and state building codes as well as the Unified Facilities Guide Specifications (UFGS). Many states and regions already reference the ASHRAE Guideline 12-2000 for Legionella. Changes to code take time, but ASHRAE Standard 188 will soon be the measure of industry best practice and used to determine legal due diligence should a case be suspected from the facility water system.

Sludge and microbio build-up in cooling tower basin.

What Does this Mean for Facility Managers?
ASHRAE Standard 188 requires implementation of a risk management process called Hazard Analysis Critical Control Point (HACCP). Any facility that meets the Standard’s criteria will require a HACCP Program.

HACCP requires that a facility owner form a team—sometimes referred to as a “Water Management Team” (WMT)—to facilitate both the creation of the HACCP Plan as well as to facilitate the ongoing validation and verification of the water system. This is not a plan that can be created and put on the shelf. Rather, the HACCP Plan defines a process that must be continually monitored and adjusted as necessary.

HACCP is actually the most widely used risk management process in the United States and globally. All food service operations use it to prevent environmental-source diseases from harming people. The process systematically addresses and documents the answers to three key questions:

  1. What are the hazards in the facility?
  2. How are the hazards being controlled in the facility?
  3. How do we know that the hazards have been controlled in the facility?


The HACCP plan answers the last question by using validation and verification. Validation is defined as evidence that a hazard has been controlled or eliminated. The most defensible way to validate performance is through water testing for the hazard (such as Legionella). Verification is defined as evidence that the HACCP program is correctly implemented. A key point that HACCP emphasizes is that validation and verification should be independent from suppliers of water treatment products and equipment.

Can Improving Safety Truly Reduce Costs?
With this increased focus on the safety of building water systems, how can facilities address the new ASHRAE requirements within existing operating budgets? The good news is Standard 188 has defined the process by which facilities can prevent waterborne pathogen disease; the purchase of capital equipment or treatment systems is neither a requirement, nor necessary in most cases. Furthermore, a “by-product” of the HACCP process is the uncovering of ways to improve the operational efficiency and sustainability of potable and utility water systems.

Water-related inefficiencies and treatment program costs are often highest when water safety is poorest. This is especially true if water and energy waste is due to microbial fouling or mineral-based scale buildup in the system. That can result in a 10 percent to 15 percent loss in heat transfer efficiency, which can significantly increase energy costs. Simply put, the best first step to improve water system safety is to reduce any inefficiency in the system.

Another view of heavy mineral scale and microbio fouling in a high efficiency honey-comb tower fill.

The reduction of inefficiencies in the water system and in the water treatment program can be achieved through better use of water pre-conditioning; more economical and more effective water treatment practice; and closer attention to water and energy conservation. Cost savings derived from better water management can then be used to improve the safety of the water system through the HACCP process.

Review is Critical
Typically, more than 50 percent of total water usage in a facility, campus or base can be attributed to the operation of the heating and cooling systems. The numbers rise as high as 75 percent to 80 percent of water usage during the warmest summer months. Along with high water usage and the potential for waterborne pathogens, reviewing the utility water systems is very worthwhile during the HACCP analysis phase. Important actions to consider taking include:

  • Maximize cooling tower cycles through management of total dissolved solids/conductivity levels. Reducing the amount of makeup and blow down water will also result in reduced chemical usage, thus decreasing the environmental impact of operations.
  • Take advantage of evaporation credits for cooling towers.
  • Eliminate leaks in heating and cooling closed loop systems, notably steam and condensate lines. Returning the maximum possible amount of condensate will significantly reduce the amount of water that needs to be converted to steam.
  • Utilize water meters across the utility systems to not only identify leaks but also verify water costs. Water metering can direct the Water Management Team to areas that present the biggest payoff from a sustainability or safety perspective.
  • Use reverse osmosis (RO) for boiler water pre-treatment. This will allow the boiler to run significantly higher cycles compared to a standard softener approach. This equipment solution can provide a significant return-on-investment (ROI) depending on the percent condensate return of the steam system. In addition to water/energy savings, chemical usage can also be reduced. RO reject water can then be re-used as cooling tower makeup water.
  • Investigate potable water usage. Some 20 percent to 30 percent of a facility’s water usage is from sinks, showers, toilets, and kitchen areas. There are many new solutions on the market to save potable water, but it is critical that these solutions, when implemented, do not worsen water quality or safety. Low-flow devices often reduce usage in hot water circulating loops to the point where the loop becomes an incubator for waterborne pathogens.

Some potable water solutions that can be effectively and safely implemented when managed as part of a HACCP program are:

  • Identify any water streams that can be centrally piped back for reuse in cooling tower makeup water (RO systems for hemodialysis or other high-purity systems, equipment cleaning/processors, etc.)
  • Utilize devices that reduce the flow rate for kitchen sprayers, improving their cleaning ability and reducing water usage.
  • Consider energy-efficient dishwashers and cleaning systems as well as any cooking systems that require significant amounts of steam, determining ROI payback for replacements.
  • Consider hands-free controls only for those hospital water systems where usage is highest in order to prevent issues from stagnant/low flow areas. Be sure to consider the operational resources needed to maintain the hands-free controls (IR, foot pedals, etc).
  • Consider low-flow or waterless toilet fixtures, again only when maintenance resources can support the systems.

Close-up view of mineral scale build up.

The requirements of ASHRAE Standard 188 will not only help facilities prevent disease from waterborne pathogens such as Legionella, but will give well-organized Water Management Teams an opportunity to review their current water systems and treatment programs.

This review, if done properly with the assistance of unbiased experts, will result in the identification of ways to reduce the water, energy, chemical and labor used by facilities to operate and maintain their capital equipment while improving its lifespan at the same time. Many, if not all, of the operational changes made as a result will help meet mandated water and energy reductions goals, and improve quality of living conditions for countless residents.

Capt. Michael P. Doyle, P.E., LEED AP, USN (Ret.), is Vice President of Operations, and Melissa Cain is Regional Manager, Phigenics LLC. They can be reached at 630-717-7546, or This email address is being protected from spambots. You need JavaScript enabled to view it.; and 414-573-1114, or This email address is being protected from spambots. You need JavaScript enabled to view it., respectively.