Five Things You Need to Know About Legionella Control

By Cody Mack, Caleffi North America

Here are five things you need to know about controlling Legionella bacteria.
What do these scenarios have in common?

You’re called out on an emergency for a damaged underground service line serving a shower in a seasonal bathhouse and find it full of foul-smelling, murky water. While on a maintenance visit at an older multi-family building you discover a neglected filtration system. Or perhaps you’re asked to help design and install a potable water plumbing system for a new assisted living facility, taking into consideration any elevated risks for the residents.

In situations like these, one word should leap to mind – Legionella.

A great deal hinges on the ability to detect and manage this sometimes-deadly bacterial contamination, such as safeguarding health and safety, professional integrity, and even avoiding potential legal liability.

Here are five things you need to know about controlling Legionella bacteria.

1. Legionella bacteria is found in almost all natural and “fresh” water sources.

Although concentrations can vary greatly, often it’s so low that no real risk is posed, even within piping systems in residential and commercial buildings when managed properly.

What are the main factors that cause Legionella bacteria to proliferate? Legionella bacteria multiply with nourishment from sediment, scale and biofilms. The bacteria are dormant below room temperature.

In warm potable water, specifically between 68 degrees and 122 degrees, the bacteria start to multiply. Stagnant water is another compounding factor, as the disinfectants added by the municipality will have lost effect in dead legs and fixture runouts. DHW recirculation is helpful to reduce the stagnation scenarios.


2. Misconceptions about Legionella abound.

For instance, there are a couple of ways a person can contract Legionnaires’ disease or, the milder affliction, Pontiac fever. It’s important to note that drinking contaminated water will not cause the disease. The bacteria have to be aerosolized and inhaled to contract Legionnaires’. In rarer cases it can be contracted by aspirating contaminated water.

Medical professionals sometimes mistake Legionnaires’ for a common case of pneumonia. Due to the lack of awareness and testing, it’s often misdiagnosed. The dangers are serious. The death rate is about 1 in 10 and there are most likely tens of thousands of cases annually in the United States.

It may also be counterintuitive to consider that the rising use of water conservation methods has contributed to the increase of Legionella. Components like low flow fixtures can increase the “water age” in a building, meaning chemical control methods like chlorine may be at low concentrations in the most hydraulically remote fixtures. Consequently, the number of cases has dramatically increased over the past 15 years.


3. Inhaling aerosolized water is the most common way by far of contracting Legionella disease.

Showers, humidifiers, cooling towers, spas, and decorative fountains create a fine mist of water droplets in the air. These areas can provide an undetectable and sometimes deadly source of Legionella. Proper preventative measures are critical.


4. When fighting the battle against Legionnaires’ disease, you are not on your own.

ASHRAE Standard 188, known as “Legionellosis: Risk Management for Building Water Systems” was first published in 2015. It is a voluntary consensus standard “…intended for use by owners and managers of human-occupied buildings and those involved in the design, construction, installation, commissioning, operation, maintenance, and service of centralized building water systems and components.”

It establishes a baseline for the development of a Water Management Program that includes analysis, control, monitoring, corrective actions, and documentation. When written into project design documents, and effectively managed, it will help reduce the danger of Legionnaires’.


5. What is the safest and most cost-effective solution to control Legionella in commercial hot water systems?

The answer is a thermal disinfection system that uses a digital point of distribution mixing valve.

This method uses a digital mixing valve with a thermal disinfection scheduling program to automatically increase recirculated water temperatures. Commonly, with temperatures on the domestic hot water return maintained above 140 degrees for a minimum of 30 minutes before returning the water to normal operating temperature.

This approach lets you forego common concerns with the use of chemicals for disinfection, such as drinking water that smells like a municipal pool and potential government oversight that may come with adding chemicals into a potable water system.

Using high temperature water circulation is safe when the system is designed and built for elevated temperatures and includes scald protection devices at all points-of-use. These devices are typically thermostatic mixing valves that are designed, tested and in compliance with standards such as ASSE 1070 “Performance Requirements for Water Temperature Limiting Devices” or ASSE 1016 “Automatic Compensating Valves for Individual Showers and Tub-Shower Combinations.”

An advanced electronic mixing valve used for thermal disinfection will have features such as an automatic, calendar based scheduling program for disinfection, alarm and data logging functions, a self-cleaning mechanism, and high flow capacity.

Controlling Legionella with thermal disinfection is a global time-tested method that will bring peace of mind to anyone involved by helping keep potable water safe for building occupants.

Temperatures between 95 degrees and 115 degrees are prime territory for Legionella bacteria to grow. Temperatures in a water system have to reach more than 131 degrees to kill bacteria, with a recommended temperature of more than 158 degrees to effectively disinfect equipment.
Cody Mack
About the Author: Cody Mack has nearly 20 years’ experience as an installation contractor, service technician, application engineer and most recently as national training manager for Caleffi North America. He pounds the pavement training on the proper use and application of product, helping you to get the most out of your systems. He can be reached at