Architectural Record BE - Building Enclosure

Meeting New Water Quality Mandates in Health-Care Settings

New national standards target reducing the risk of Legionnaires’ disease
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Sponsored by Watts
By Peter J. Arsenault, FAIA, NCARB, LEED AP

Water Distribution Components

Once the water is in the facility, it needs to be distributed appropriately for use on demand. Depending on the size and nature of the facility, that may prove to be rather complex, which is why the schematic flow diagram of a water system is important as part of a water management program. We will look at some of the common components of a distribution system here.

  • Cold water storage tanks: Some facilities with high water flow requirements will use an on-site water storage tank to buffer the demand with the usage. That is an appropriate and time-honored method, but keep in mind that such tanks can also be a breeding ground for legionella and other bacteria. Therefore, the temperature of the water should ideally be kept below 68 degrees Fahrenheit to keep legionella dormant without the risk of activity.
  • Hot water heaters and tanks: Water in a hot water tank is generally kept at an appropriate temperature for warm or hot water use in a building at around 110 to 120 degrees Fahrenheit. Unfortunately, that temperature can also be in the ideal range for legionella bacteria to grow and thrive. If the temperature hasn’t been appropriately raised to the ASHRAE-recommended 140 degrees Fahrenheit to kill legionella within 30 minutes, then there is the risk of bacteria growth. This will need to be addressed and monitored or the water tanks will need to routinely heat up to these kill-range temperatures to protect against any growth or spread of legionella.
  • Mixing valves: While heating water to the rapid-kill range is one of the most effective and reliable control measures for dealing with legionella, it is not necessarily the best temperature for heated water to be used by people. On average, any water that is above 106 degrees Fahrenheit will cause scalding and pain in humans, while water that is 140 degrees Fahrenheit can cause third-degree burns in a matter of seconds. This is why plumbing codes limit the maximum temperature exiting a fixture at 120 degrees with the expectation that people can readily control the mix of cold and hot water at the faucet to meet their needs. However, there are plenty of things that can change the water temperature coming out of those faucets. For example, it is common for a health-care building to use a recirculating system that pumps hot water uniformly through the hot water piping to prevent long wait times for heated water at a faucet, etc. However, things like pressure fluctuations can cause hot and cold water to move less predictably through the system, while valves in the system could malfunction or fail. Mixing valves helps compensate for those discrepancies and deliver a more predictable water temperature output.

Clearly, it’s important to meet both the needs of killing legionella with higher-temperature water and the human requirements of a lower, useful temperature. The solution is found in the use of tempering valves or mixing valves that blend hot water (generated and stored at temperatures high enough to kill bacteria) with cold water in a controlled manner. This ensures constant, safe outlet temperatures while minimizing the occurrences of both scalding and legionella.

When looking at mixing valve systems, there are two fundamental types. A point-of-source (POS) system locates valves at or near the water-heating source and typically has a higher capacity for controlled temperature water. A point-of-use (POU) system uses multiple, smaller mixing valves at or near plumbing fixtures, such as showers, lavatories, whirlpools, and emergency fixtures. Both types are common and have a range of standards issued by the American Society of Sanitary Engineers (ASSE) relevant to particular usage.

Thermostatic mixing valves

Thermostatic mixing valves can be installed and used as a point-of-source system (left) or as a point-of-use system (right).

  • Digital mixing systems: Beyond purely mechanical mixing valves, computerized digital mixing systems are also available that are considered a smarter and safer way to deliver mixed water throughout a health-care facility. In this type of system, intelligent control modules and electronically actuated valves are used to allow faster and more accurate response to constant changes in the mixed water delivery demands, often anticipating system changes before they occur. Further, digital water mixing and recirculation solutions can be integrated into a building automation system to allow facility managers compete control of and visibility into their domestic hot-water delivery.
digitally controlled temperature-mixing system

A digitally controlled temperature-mixing system provides the most accurate control of water temperature in buildings.

As a point-of-source system, a digital mixing and recirculation station can provide precise control of hot water delivery within 2 degrees of the set point, surpassing industry standards for mechanical systems. Further, it eliminates temperature creep within the system, thus eliminating the need for balancing valves. All of this means that it can more precisely be controlled to mitigate legionella growth in the heated water. In particular, a sanitization or disinfectant mode can be triggered to briefly raise the temperature above 158 degrees Fahrenheit to induce a “rapid kill” and purge all legionella bacteria. At the same time, the digital mixing system can control temperatures leading to faucets, showers, etc. to reduce the risk of scalding in the mixed water. If combined with separate point-of-use protection, then it allows for continuous elevated circulation temperatures to prevent legionella per ASHRAE and CDC guidelines. Concurrently, the digital system can control the circulation pump to prevent stagnant conditions or maximize flow rates. Finally, since most large facilities use some type of building automation system, a digital mixing system can be linked to the larger system to communicate and control temperature, pressure, flow, and energy consumption as part of an overall operations and maintenance plan. It also makes documentation and verification more straightforward in a water management program as called for in ASHRAE 188. From a specification standpoint, most of these systems are easy to install since they typically come pre-piped, pre-wired, and tested, allowing them to carry a warranty from the manufacturer for up to five years.

  • Pipes, valves, and fittings: If all of the measures described thus far are followed, then the water flowing through the distribution piping, valves, and fittings should be fairly safe, but that doesn’t mean they don’t need to be checked, inspected, and verified as part of the water management program. Valves of all types in particular can be a concern, so working closely with manufacturers to identify and specify those that are most suitable for preventing problems and growth is appropriate.
  • Faucets and wash stations: The point-of-use fixtures are where people come in contact with water throughout the health-care facility. The primary concern is that a biofilm of bacteria can start to form on edges or within components of a faucet or wash station. If that bacteria is allowed to build up in things such as aerators or faucet flow restrictors, then it could either build up and grow, or worse, be sprayed into the air and cause illness. That means such components need to be checked, cleaned, or replaced regularly. A related concern is the location of wash fixtures and the potential for water splashing onto either people or equipment used to treat patients. Separating sinks and other water stations from medication dosing areas, and equipment is one way to help minimize the possibility of cross contamination. Using splash guards around sinks and scrub areas can also be effective in some areas.
diagram: digitally controlled temperature-mixing system

The points where people come into contact with water in a facility is where legionella and other bacteria can be released from a biofilm buildup or sprayed into the air and breathed in.

  • Showerheads and hoses: Showers and hoses pose additional concerns since biofilm formation can be particularly problematic here. Handheld showers are common in health-care facilities, but the hose portion can hold water between uses, and the showerhead itself can remain warm and moist, allowing bacteria growth. The recommendations here include allowing the hoses to hang down and drain after each use. It is also prudent to replace handheld showers periodically.

Drainage Systems

The final part of a water management program includes attention to the drainage systems in a building. Since virtually all of the water that flows through a facility is used and then drained away (except for drinking or evaporation), the drainage system needs to be free of legionella and other bacteria as well. This means that water must be freely draining with no opportunity for stagnation or biofilm formation here either.

When it comes to drainage piping, nonporous materials are preferred in health-care facilities. Porous materials, such as some metals and plastics, can become unintended breeding grounds for bacteria growth. Significantly lower growth of bacteria has been found on stainless steel, making it the ideal solution for applications where hygiene is a concern, particularly in kitchens and food service areas of health-care facilities.

Stainless steel drainage

Stainless steel drainage components remain cleaner and less likely to contribute to bacteria growth.


Outbreaks of illness, particularly Legionnaires’ disease, can be dramatically reduced or potentially eliminated in health-care settings if proper attention is paid to the important aspects of water management. The protocol and requirements of ASHRAE 188 are recognized by facility managers and governmental bodies as the best place to start since it is based around a comprehensive and continuous water management program. In fact, continued accreditation and funding for a facility under Medicare and Medicaid may depend on it. Reviewing and addressing all components and opportunities in the supply, distribution, and drainage portions of a building water system is needed to produce a proper program. Ultimately, it is the collaboration of design professionals, facility managers, equipment suppliers, and others that allow for the successful development and ongoing monitoring of an effective water management program.

End Notes

1“Legionella (Legionnaires’ Disease and Pontiac Fever).” Centers for Disease Control and Prevention. 2 June 2017. Web. 14 August 2017.

Peter J. Arsenault, FAIA, NCARB, LEED AP, is a practicing architect, green building consultant, continuing education presenter, and prolific author engaged nationwide in advancing building performance through better design.

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Watts is a global leader in the design and manufacture of innovative water solutions for residential, commercial, and institutional environments. Products include an extensive line of flow control, filtration, and treatment products for water quality and residential plumbing and heating. Founded in 1874, Watts is headquartered in North Andover, Massachusetts.


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Originally published in Architectural Record