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CDC Sampling Procedure and Potential Sampling Sites
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www.cdc.gov/investigate-legionella/
SAMPLING POTABLE WATER AT THE POINTS OF USE
Note: In most situations, it’s appropriate to sample only the hot water. However, there are situations where taking some cold
water samples is helpful. For example, in hot climates, the cold water may be warm enough for rapid Legionella amplification
(>77°F). Desalination may also elevate cold water temperature. Cold water could also be warm due to lack of insulation
between hot and cold water pipes.
Collect one biofilm swab and one bulk water sample from each sampling site (i.e., each showerhead or faucet).
1. For showers, ask facility maintenance personnel to remove the showerhead. For faucets, ask them to remove the aerator.
Take biofilm swabs:
2. Turn on the water for a couple of seconds to moisten the pipe, and then turn it off. Insert a sterile Dacron- or
polypropylene-tipped swab deep into the faucet/pipe. Try to get beyond the bend and swab around the inside surface
firmly without breaking the swab stem. (If there is visible biofilm on the inside of the showerhead or faucet aerator when
these are removed, they can also be swabbed.)
3. Place the swab into a 15 mL sterile plastic tube and add 3–5 mL of water from the same faucet to keep the swab tip
moist during transport. Snap the wooden or plastic swab stem approximately 1 in. from the top of the tube. Add a drop of
0.1N sodium thiosulfate solution to neutralize residual disinfectants. Tighten the tube top to prevent leakage.
4. Label the tube with a unique identifier. Record the type and location of the sample on a Sample Data Sheet, and place the
tube into a cooler.
Take bulk water samples:
5. After the biofilm swab is collected, turn on the water and let it run until the water is warm but not hot. The goal is to
obtain water currently in the piping behind the fixture along with any material shed from biofilm. Avoid heating water
excessively (approximately 122°F or higher) since free-floating Legionella will die quickly at elevated temperatures.
Collect 1 L of water from the faucet into a sterile 1 L bottle, leaving a 1 in. space at the top.
6. Add 0.5 mL of 0.1N sodium thiosulfate solution to the water sample to neutralize residual disinfectants. Tighten the bottle
top to prevent leakage.
7. Label the bottle with a unique identifier. Record the type and location of the sample on the Sample Data Sheet, and place
it into the cooler.
Measure water parameters:
8. Run the hot water until it is as hot as it will get. Collect 100–300 mL of water in a separate plastic sampling bottle. The
same bottle can be used for measuring water parameters at every sampling site. Measure temperature, pH, and chlorine
level of the sample. Record all measured data on the Sample Data Sheet. If it takes more than a minute for the water to
get hot it could indicate a local problem, such as with a mixing valve, or a system-wide imbalance.
SAMPLING POTABLE WATER AT THE HOT WATER HEATERS
1. Collect a bulk water sample only; it is rare that a biofilm sample can be obtained from a hot water heater since this would
require completely draining the tank.
2. Ask facility maintenance personnel to open the drain valve of the hot water heater and collect 1 L of water into a sterile
1 L bottle, leaving a 1 in. space at the top.
3. Add 0.5 mL of 0.1N sodium thiosulfate solution to the water sample to neutralize residual disinfectants. Tighten the bottle
top to prevent leakage.
4. Label the bottle with a unique identifier. Record the type and location of the sample on the Sample Data Sheet, and
place it into the cooler.
5. Always measure and record the temperature, pH, and chlorine level of a bulk water sample collected from a hot
water heater.