Monitoring Building Water Quality to Reduce Risk and Stay in Legionella Compliance

Updated November 6, 2024

Monitoring domestic (potable) water for conditions conducive to Legionella growth has been recommended by the Centers for Disease Control and Prevention (CDC), most US state health departments, and the Association of State Drinking Water Administrators. It is also required to comply with ASHRAE Standard 188, Joint Commission Standard EC.02.05.02, and the Veterans Health Administration (VHA) Directive 1061. 

Water quality monitoring makes water management programs (WMPs) more protective, predictive, and insightful. If the monitoring is automated, it also makes WMPs easier. Based on a 2021 study of more than 900 water management programs, making it easier to fully implement a comprehensive WMP is important for reducing legionellosis and other illness caused by pathogens in building water systems (Freije 2022). 

Water Quality Monitoring Versus Legionella Testing

Water quality monitoring is not a surrogate or substitute for Legionella testing. And, Legionella testing without water quality monitoring provides too little data for protectively managing building water systems.

Although Legionella testing can provide valuable “bottomline” data, the test results do not indicate the conditions (e.g., inadequate temperatures, flow, or disinfectant residual) that may have led to Legionella growth. Monitoring water quality is needed to frequently check conditions that can affect Legionella growth. 

Also, Legionella tests do not alert a facility to an incident or condition that may require an immediate response. For example, if heavy construction or water pressure shock releases sediment or films into a building’s domestic (potable) plumbing system, which could cause an outbreak, Legionella testing will not alert the facility in time to respond because Legionella tests cannot practically be performed several times a day, and even if they could, culture results would take too long to provide a timely alert. 

What Water Quality Parameters to Monitor

ASHRAE 514 Appendix F suggests monitoring for (a) temperature, pH, conductivity, disinfectant residual, and turbidity in piping at one or more POEs, (b) temperature in cold-water storage tanks, (c) temperature at master thermostatic mixing valve (TMV) outlets, and (d) temperature and flow at water heater outlets, hot-water recirculation lines before return at the water heater or hot-water storage tank, and each hot-water return balancing valve.

Consider monitoring the following parameters:

a. Conductivity and turbidity at the building point of water entry (POE)

Conductivity correlates with total dissolved solids. Turbidity is a measurement of water cloudiness caused by microscopic particles (total suspended solids). Conductivity or turbidity readings significantly outside the typical range in the public water supply can indicate a problem that requires an immediate response. 

Events such as water main breaks, water pressure shock, a change in the city’s source water, intrusion of rainwater, flooding and other extreme weather events, fire hydrant use, heavy construction, or problems with the water utility’s treatment processes can dislodge biofilms or introduce contaminants that cause a spike in conductivity or turbidity.

By continuous monitoring conductivity and turbidity with sensors, the water management program team may be able to respond quickly enough to prevent illness caused by Legionella amplification associated with such events.

b. Water Temperature

Temperature affects pathogen growth. 

The purpose of checking temperatures is not merely—or even primarily—to determine whether temperatures are within the Legionella growth range. 

Keeping temperatures outside of the Legionella growth range may not be an option because of scalding risk, or feasible in every part of a domestic water system. Temperature management is important but will not guarantee Legionella control. However, it is important to know the temperature of the water entering your building during each season and to maintain domestic water temperatures within target ranges.

Relationships are also important, to uncover system deficiencies. For example, it is beneficial to know the heat gain in the cold water between the point of entry (POE) and points of use (POUs), and the heat loss in the hot water between water heater outlets and POUs.

c. Disinfectant residuals

Disinfectant levels affect pathogen growth. Disinfection effectiveness depends on the disinfectant, pH, the residual concentration of that disinfectant, and the pathogen. Not all common waterborne pathogens respond the same to a given disinfectant. Each type of bacteria requires a certain concentration and contact time.

Testing disinfectant levels at POEs is important to know what disinfectant residual is being provided in the public water supply at various times of the year, and to alert the WMP team of inadequate levels.

Testing at POUs shows whether a disinfectant residual is maintained throughout the system, and how much is lost on the way from POEs to POUs. Disinfection occurs only with the residual left after an oxidant (e.g., chlorine) reacts with metals, organics, and nitrogen compounds. Tests of various locations can help to identify areas where bacteria or corrosion might be consuming disinfectants–giving valuable insight for smarter water system management.

To avoid chemical hazards, testing is important also for ensuring disinfectant residuals are not too high, particularly in systems with supplemental disinfection.

d. Water pH

pH affects disinfection effectiveness for some chemicals and metal ions. Some disinfectants are effective at a wider or different pH range than others. The effectiveness of chlorine and copper and silver ions is especially dependent on pH. The form of chlorine that kills bacteria in water — hypochlorous acid (HOCI) — decreases as pH increases.

pH also affects corrosion and scale. pH can be tested manually with test kits or automatically with sensors.

It is typically sufficient to test pH only at POEs. Facilities should know the incoming pH level, particularly to be prepared to carry out emergency disinfection or to monitor the effectiveness of continuous supplemental disinfection.

e. Water Flow

Water age (stagnation) must be managed for the control of Legionella and other pathogens.

Consider monitoring three flow metrics:

• Water volume at POEs. This is especially important in buildings supplied with more than one line from the public water main. Keep all feeds open and monitor the water volume of each feed to ensure adequate use, either by installing a flow meter/sensor or by checking monthly water bills. 
• Water flow rate in hot water recirculation piping. A flow rate that is too low—due perhaps to hot water recirculation pumps that are off or under-sized—increases water age.  Excessive velocity can cause corrosion and equipment damage by erosion.
• Water use time at POUs. The key flow metric at POUs is the amount of time that hot and cold water is run over a period of days. For example, installing sensors to monitor the times that POUs are used, and the duration of each use, can help a facility ensure each is used enough, without wasting time or water by flushing more than necessary. 

Regulations or standards may dictate additional parameters to monitor (see table).

Water Quality Monitoring Requirements and Recommendations

How to Monitor Water Quality Parameters

Water quality parameters can be monitored manually, with test kits or handheld instruments, or automatically with sensors. Sensors are preferred, to minimize labor, monitor more frequently, and get more data, but sensors are not available for all parameters.

Handheld devices may be more practical at POUs, especially in facilities that have no building automation system. Handheld devices may also be required to get measurements needed to comply with supplemental disinfection system regulations.

David Swiderski is the Senior Technical Strategist, and Matt Freije the CEO, at HC Info.

This article was excerpted and adapted from the LAMPS Training article “Water Quality Monitoring: Parameters, Locations, Targets, Limits, Alarms, Methods.”

What other water quality parameters do you think should be monitored in building water systems for Legionella control?