Although many Legionella outbreaks have been attributed to building heating and cooling systems, literature indicates that the majority of all Legionella outbreaks are related to a building’s domestic hot water system. The domestic hot water system in buildings such as hospitals, schools, nursing homes, etc. provides an excellent environment for Legionnaires’ disease bacteria. Warm water temperatures in the ideal growth temperature range, stagnant areas, dead ends, pipe scale and biofilm, etc. cause the essential ingredients and a food source for bacteria growth.
A chemical process was developed using a safe, food-grade item that can be added to and injected along with chlorine to protect the pipe surface. It seals it, coats it, isolates the bacteria, enhances the disinfection process and provides protection against corrosion that would normally be caused by continuous chlorine injection. The process also controls leaks, rust and scale in galvanized piping, pinholeing in copper piping and reduces lead in the water supply.
Legionnaires’ disease bacteria can be easily controlled by maintaining the water temperatures above or below the ideal Legionella Bacteria growth range of if the temperature will be in the ideal growth range continuous injection of chlorine between 0.5 and 2 parts per million can control microorganism growth. (consult a water treatment professional for the correct chlorine level based on the water quality in your area.) Chlorine is effective and universally accepted as a water treatment chemical disinfectant for potable water systems. Chlorine is relatively inexpensive and readily available. Other treatment chemicals like chloramines and bromines are available. For water features, pools and fountains and other non-potable water systems other treatment methods are available including: Ozone, Ultra-violet light, Copper-Silver ionization, etc.
Even if the storage tank is removed, or not used without making other changes, the piping system will still have many dead legs. The water mains and branch lines remain with dead legs. All the problems (dead ends, stagnant areas, corrosion, etc.) in the piping system would remain the same. When there is water hammer, flow surges and other disruptions in the piping system, the flow stream dislodges sediment, scale and bacteria laden biofilm from the wall of the piping and distributes the bacteria throughout the downstream piping system. Maintaining hot water circulation temperatures a few degrees above 122 degrees Fahrenheit, and/or continuous supplemental treatment with chlorine or other water treatment chemicals, can keep the return lines from becoming re-infected with growth of microorganisms like Legionella.
Storage tanks can be used in hot water systems as long as the hot water in the tank is stored at or above 140 degrees Fahrenheit and temperature limiting devices are installed and adjusted at the various fixtures to prevent scalding.
A high temperature flush does kill the bacteria if you can get the temperature high enough and if you can draw 160 degrees Fahrenheit throughout the whole system. It is not a permanent solution – It is only a temporary cure in systems that are capable of being fully flushed at 160 F. Unless you can maintain the high temperature and bring 160 degree Fahrenheit water to each and every fixture, dead end and stagnant area in the building, the bacteria will be reseeded. Most instantaneous water heating systems are not sized to produce 160 degree Fahrenheit hot water for long periods of time. Storage water heaters will often run out of hot water before the entire piping system is flushed for the required duration. Consider the costs in terms of manpower to have people stationed throughout the facility to flush each and every hot water outlet and energy costs. Consider the possibility of scalding during the many hours of elevated temperatures in larger buildings. Consider the effect the high temperature will have on the corrosion and scale on heating surfaces in the hot water system.
Many sites and sources claim that you can’t get Legionella from a shower head but this is not true! Legionella is transmitted to the victim by aerosolized water droplets from a contaminated water source. Hot water stored in the ideal growth temperature range can grow or incubate Legionella bacteria into large numbers. When the contaminated water is aerosolized in a shower head and inhaled by the victim, they inhale the bacteria laden water droplets into their lungs. Newer Ultra-low-flow shower heads break up the water into a fine mist which can be easily inhaled. The mist can transport Legionella bacteria into the lungs. The lungs serve as a medium or petri dish for the bacteria to grow on where it infects the lungs first, causing pneumonia where the victim will experience flu-like symptoms. As the disease takes over the body, various organs shut down causing severe disabilities and in many cases death.
With 35 years of experience designing plumbing and mechanical systems for several major architectural, engineering, and design & construct firms. He has designed plumbing, mechanical, and fire protection systems for all building types including airports, stadiums, industrial manufacturing facilities, office buildings, commercial and retail buildings, hospitals, laboratories, prisons, jails, hotels, apartment buildings, military projects, high rise and educational facilities.