Section II:C-2. Domestic Cold-Water Systems
Domestic cold-water systems are not a major site for Legionnaires' disease bacteria (LDB) growth. However, elevated levels of LDB have been measured in ice machines in hospitals. Cold-water lines near heat sources in the units are believed to have allowed the bacteria to multiply. Dental water lines have been recognized as sources of water contaminated with high concentrations of microorganisms including LDB. However, an increased risk of disease among dental staff or patients has not been demonstrated.
Which cold-water systems have been recognized as a source of LDB contamination?
Under most circumstances, evacuation of the building is not recommended. However, with confirmation of an outbreak individuals with compromised health conditions
should be considered for removal from the implicated building. Individuals at high risk for contracting the disease include:
|Fig.1: Dental water
lines may be a source of contamination
- Ice machines in hospitals supplied by cold-water lines near heat sources
that promote LDB growth.
- Water tanks that allow water to remain uncirculated for long periods also
can promote bacterial growth.
- Cross-contamination of a domestic cold-water system with another system
should always be suspected of promoting bacterial growth.
- Emergency water systems such as fire sprinkling systems, safety showers,
and eye wash stations are other domestic cold-water sources from which LDB have been
cultured. These systems experience little water flow and can be subject to periods of elevated
temperatures. In addition, operation of these devices will aerosolize water. For these reasons,
emergency water systems should be considered potential sources of LDB, although no documented cases of
legionellosis have been associated with these sources.
- Operating conditions for dental water lines are especially appropriate for
LDB proliferation because the water is stagnant a majority of the time, the narrow plastic tubing
encourages bio-film formation, and the water temperature is usually 20°C (68° F) or higher -- some
systems maintain water at 37°C (98°F).
- Filtration of water at the point of use with replaceable, in-line, Food
and Drug Administration (FDA) approved, 0.22-micrometer pore size filters is recommended for
minimizing risk to patients and staff in dental facilities.
do I maintain a cold-water system?
Maintaining cold-water lines below 68°F (20°C) will limit the
potential for bacterial growth. Other methods to consider include the following:
|Fig.2: Flush safety
- Maintain residual chlorine levels as per local authorities recommendation.
- Eliminate "dead leg" sections or frequently flush taps to drain stagnant areas to limit
growth of the organism.
- Eliminate or design stagnant tanks to reduce storage time to one day or less.
- Cover cold-water lines to prevent contamination and protect them from temperature extremes.
- Protect all connections to process water with a plumbing code-approved device such as a back-flow
preventer or air gap.
- Flush safety showers and emergency eye wash stations at least once a month.
often to test cold-water systems for LDB following identification of contamination?
When treatment steps are successfully completed, return the water system to normal operation but test it
for LDB according to the following schedule:
- Weekly for the first month after resumption of operation.
- Every two weeks for the next two months.
- Monthly for the next three months.
- If tests fail, repeat the disinfection procedure and restart the test program.
do I collect cold-water samples?
|Collect water samples to determine
potential contamination, as outlined above. Note: It is important not to
flush the outlet before taking a sample because the end section of the water system may be a source of
Water Sampling Protocol: Sampling information
specific to cold-water systems is provided below. For more information about water sampling, please refer
to Section II:E. Water Sampling
- Sample the incoming water supply if the plumbing provides access.
- Sample cold water tanks and reservoirs if any.
- Sample faucets and showerheads throughout the facility, for example, those nearest, intermediate,
and most distant from storage tanks and connections with municipal water supplies.
- If a biocide is used, follow the manufacturer's instructions for proper neutralization.
- The OSHA suggested guideline for LDB in domestic cold-water systems is less than 10 CFU per
- If LDB concentrations are below 10 CFU per milliliter and no LDB were detected in swab or other
samples, no further monitoring for LDB is necessary. Continue the maintenance program as long as the
system is in use.
- If water concentrations exceed 10 CFU per milliliter or LDB were detected in other samples, take
steps to identify the source of contamination or amplification and treat the system
See How to treat a contaminated
- Sample the water system monthly until the source of contamination is identified and adequately
treated. Once LDB concentrations remain below 10 CFU for a tree-month period, sampling may be
How to treat a contaminated cold-water system
Cold-water systems have no provision for heating water, therefore, disinfection
cannot be by heat treatment. The treatment procedure below should be used if cold-water systems are shown
to contain measurable LDB or are assumed to be contaminated based on epidemiological evidence.
Flush cold-water outlets.
- Clean then disinfect all cold water systems including storage tanks, drinking fountains, water
lines, and water outlets, as follows:
- Use an accepted chemical disinfectant such as chlorine or other acceptable biocide and follow the
- Use other technology that has been shown to be safe and effective.
- If the cold-water lines have significant contamination, hyper-chlorination can eradicate LDB.
- Raise the level of free chlorine to 20-50 mg/L and maintain this concentration for one hour at 50
mg/L or for two hours at 20 mg/L.
- Faucets are then allowed to run until the odor of chlorine is present, and the water is allowed to
remain for approximately two hours.
- Flush all cold-water outlets and fountains for four minutes to remove disinfectant, at least twelve
hours before re-use.