How is a Building Water System Contaminated?

Legionella is a type of bacterium found naturally in fresh water lakes and streams. Much of our potable (drinking) water is derived from these sources, and municipal water treatment operators endeavor to disinfect water before it reaches points of consumption. While these efforts are highly effective, some legionella bacteria ultimately survive and make their way into building water systems. If conditions are right, Legionella can grow and multiply in building water systems; unfortunately, many buildings have ideal conditions for such growth. Warm temperatures (70 – 130F is perfect), stagnant or unused sections of piping, dead-legs, dirt and debris inside pipes, and several other factors promote the growth of “biofilms” which in turn act as a highly protective residence for the legionella bacterium. Attempts by government and consumers to reduce water usage have exacerbated the problem.

Alternative Treatments

Chlorine has long been the favored method of disinfection for water systems. Chlorine can be made available in several forms, however, and the choice of chemistry can be important. In short:

  • Sodium hypochlorite (bleach) is the simplest and most cost-effective water treatment, especially for ongoing treatment.
  • Chlorine dioxide is a very effective method for attacking biofilms. Ongoing treatment with this chemical, however, can be complex and entails significant regulation-mandated costs.

Is On Going Treatment Necessary?

In a word – yes. Once a building has been contaminated it is extremely difficult – if not impossible – to eliminate all traces of legionella bacteria. Besides that, fresh bacteria may enter the building at any time. At least some of the conditions which allowed the previous growth of biofilm and legionella colonies are likely to still exist.