Legionella
Pseudomonas
Mycobacteria
Aspergillus
Waterborne Pathogens

Many different bacteria, fungi, and parasites can be found in tap water.  Originating at the municipal water supply or local aquifer, hospital water containing low levels of microorganisms is diverted to hot and cold water supply systems.  Although different types of free-floating microorganisms may predominate in hot and cold water, they have the common ability to anchor themselves to internal pipe surfaces, faucets, and shower heads.  Once they irreversibly attach to an internal plumbing surface, they multiply and produce a sticky extracellular matrix.  This highly organized and well-characterized aggregate of numerous types of microorganisms that flourish within the matrix is called a biofilm.

Read more about biofilm

As microorganisms within a biofilm multiply and the biofilm enlarges, the shearing forces of flowing water break off microbe-containing fragments and transport them to distant locations in the water distribution system through processes known as seed dispersal, streaming, detaching, rolling, and rippling.  In this way, biofilm serves as a repository for the sustained release of bacteria into flowing water.

Patients with weakened immune systems are exquisitely vulnerable to direct contact with pathogens in contaminated water, whether it be in the form of a liquid stream, an inhaled aerosol, the ice in a beverage, contact with a staff person who has just washed her hands, or with a reprocessed medical device that has been rinsed with water.  When water enters the hospital room environment from a faucet or shower, tiny water droplets containing biofilm contaminants separate from the main water stream and are spread by air currents in all directions.  Some are then inhaled as aerosols, while others condense onto surfaces where they can be transferred to patients and staff through touch contamination.  Although these aerosols may not pose a threat to a healthy individual, they can very seriously affect the health of an immunocompromised patient.

In order to eradicate waterborne microorganisms, water systems are periodically disinfected either chemically or with extremely hot water.  Although these methods may achieve a measure of short-term success, that success rarely extends to the long-term as these methods cannot access and destroy every biofilm community, nor are they sufficient to cope with occasional bursts of elevated microbial levels in incoming water.  Additionally, in complex plumbing systems facility renovations may inadvertently lead to the creation of "dead ends" where water stagnates and disinfectants cannot attain adequate concentrations to eradicate biofilm.  Biofilm in plumbing "dead end" regions constantly seed the formation of new biofilm communities elsewhere in the plumbing system.

Advantages and Disadvantages of Systematic Water Disinfection Technologies

Systematic Water Disinfection Technology	Advantages	Disadvantages
Hot Water Flush	Good short-term efficacy No special equipment or maintenance required	Poor long-term efficacy  Difficult to reach all points of complex water distribution systems Labor intensive and expensive to perform Risk of scalding
Hyperchlorination	Good short-term efficacy	Expensive to perform / Frequent checks of chlorine levels required Amoebae are resistant / Mycobacteria & Legionella potentially resistant Microbial recolonization can occur Odor, allergic reactions, and carcinogenic byproducts (trihalomethanes) Corrosive to pipes
Chlorine Dioxide	Good short-term efficacy Fairly easy to install Low to moderate cost	Poor long-term efficacy / Difficult to maintain Does not penetrate completely into biofilms Amoebae & Legionella in biofilms are resistant
Copper-Silver Ionization	Good short and long-term efficacy Fairly easy to install and maintain	Not equally effective for all pathogens / Amoebae are resistant Water must have low concentration of dissolved solids Requires routine maintenance / Only effective with recirculated hot water Can corrode steel and galvanized pipe
Ultraviolet Light	Good short-term efficacy Easy to install Strong effect on planktonic (free-floating) Legionella No disinfection chemicals required	Moderate investment required Fair long-term efficacy / Microbial recolonization can occur Poor penetration through established biofilms Water clarity an efficacy factor / Scale buildup on lights Difficult to reach all points of the distribution system
Ozonation	Good short-term efficacy	Requires specialized ozone-generation equipment High purchase cost / Difficult to install and maintain / Damages plumbing Disinfects only at the point of injection Ozone decomposes quickly / Questionable impact on biofilms
Monochloramines	Requires specialized ozone-generation equipment High purchase cost / Difficult to install and maintain / Damages plumbing Disinfects only at the point of injection Ozone decomposes quickly / Questionable impact on biofilms	May not penetrate biofilm Residuals difficult to remove from water Amoebae are resistant / Mycobacteria potentially resistant Must be removed from water for dialysis

Reference:

"Comments on investigations on the reduction of Legionella", Der Hygieneinspektor 6/2001, Dr. Peter Schindler, German health ministry department of southern Bavaria