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Drinking Water Bacteriology: Sample Collection , Storage and Transport to the Laboratory
Introduction
Samples for analysis should be collected from regularly used cold water
taps that are representative points on the distribution system. At least a 100 ml sample must be taken using not only a clean, but a STERILE container.
Although we recommend you obtain a laboratory prepared sterile container, you may still find it necessary prepare one yourself. To
do so follow these simple directions or purchase such a container from another source (such as a doctor's office or drug store). Select a container that seals tightly, will not be harmed by boiling, and has a
volume of at least 100 milliliters (about 4 ounces). Make sure the container is clean. Then sterilize by boiling it, completely submerged, in water for at least ten minutes. Carefully remove it
from the boiling water and assemble without touching the inside of the lid or container. Allow to cool before use. This container should remain sterile until it is opened for your future sampling use.
The water must be run to clear the working parts of the valve in use and the service line. You may notice a change in water
temperature as the lines are cleared and fresh water from the main or home pressure tank/well system flows from the tap. If possible, select a tap that is supplying water from a service pipe directly connected
with the main and not, for example, served from a storage tank or cistern. Typically, in the home, the kitchen tap will usually serve this purpose. Although usually not necessary, you may wish to disinfect
taps of questionable cleanliness. To avoid damage to plastic and rubber faucet parts, it is recommended that heat be avoided and either a solution of 70% Isopropyl Alcohol (2-Propanol) or 100 mg/l or greater
Chlorine (Sodium Hypochlorite) be used. Bottles should be filled without splashing or adjusting the flow of water. Remember, bacteria may be added to the sample from fixtures, fingers, dust in the air or
poorly flushed systems etc. Once in the container, it is not possible for the laboratory to decipher where they came from and all bacteria recovered will be considered part of your water sample. If you
wish, the laboratory can arrange to have qualified personnel collect your sample properly in the appropriate containers and transport them to the laboratory under the prescribed conditions.
Sampling Procedure
1. Select a cold water tap in regular service. Do not use
leaking taps or taps that allow water to flow over the outside surface of the fixture. Prior to disinfection, or any of the steps below, remove any aerators, strainers, filters, hose attachments or purification
devices. Run the water 10 or 15 seconds to be sure no parts are retained in the faucet. Avoid using mixing type faucets if possible. If this is not possible, run the hot water for two minutes past the
water stream becoming hot, then proceed as follows.
2. If you have decided to disinfect the faucet, use either 70% Isopropyl alcohol, available from any drug store, or a dilute (at least
100 mg/l) chlorine solution (which can be prepared from chlorox bleach, for example) to rinse the faucet (once aerator or other devices are removed). Make sure the solution is used to rinse the inside and
outside of the faucet. Once applied, allow some time for it to work by not beginning the next step for a minute or two. If you must disinfect and no solutions are available, several matches may be used
effectively to do the job. Use them to flame around the faucet opening. Take care, as this technique will damage plastic or rubber parts.
3. Run the cold water faucet long enough to clear the lines and gain representative water from the main or well. In some cases
this may require up to 10 minutes depending on the flow from the faucet, distance to the main, or the storage capacity of the pressure tank etc. Usually, 3 or 4 minutes is sufficient. Run the water
heavily, but avoid splash back from the sink to the fixture. The splashed material may contain contaminating bacteria. If there are splash back problems, you may be forced to run the water longer or
disinfect the fixture again and run water for a second, but more brief period, before collecting the sample. After running water vigorously for 3 to 4 minutes, adjust the flow to a point that allows your
container to be filled without splashing and continue running at that level for another minute or two.
4. In collecting the sample, remember, you wish to have the sample container open for as short a period as possible. If you have a
Cedar Grove container DO NOT RINSE BEFORE COLLECTING THE SAMPLE. The properly prepared Cedar Grove bacteriological container contains Sodium thiosulfate that is required, in some cases, for chlorine
neutralization. To collect the sample, open the container and quickly fill it to slightly above the 100 ml fill line. Immediately close the cap (and carefully place and tighten the security strip, if one
is present).
Storage and Transportation
Samples should be stored at near freezing
temperatures. That is to say, in your refrigerator if not going directly to the lab. An ice chest should be used for transporting samples to the laboratory. Ideally, the temperature should be between
1 and 5o Centigrade, however, temperatures of up to 10o Centigrade are acceptable for transport. Remember, bacteria may multiply or die depending on temperature
considerations. Therefore, the accuracy of your lab work will not only depend on how you collect your samples, but how they are stored and transported to the laboratory.
Bacteriological analyses are run every day the laboratory is open. Please keep in mind, however, the laboratory is usually closed
on weekends and for holidays, (If you are not sure, check with our office for the laboratory's schedule of holidays.) We suggest you collect samples just before bringing the material to the laboratory in order
to avoid possible contamination, transport and holding problems. Samples will be accepted anytime from our office opening in the morning at 9:00 am, to about 3:30 pm in the afternoon of any working
day. This will allow your sample to be properly processed and it's laboratory work to begin within normal routines. In no case should the time from sampling to analysis exceed 30 hours. Due to
this fact, samples should arrive at the lab less than 24 hours after sampling. It is also assumed that such delayed delivery occurs prior to 3:30 pm on any given business day. (Again, this will allow enough
time for proper sample preparation and the analysis to begin without exceeding the 30 hour time limit or the need for overtime etc.) If you can not meet this very broad requirement, call the laboratory to check
if special arrangements are necessary to properly receive and begin work on your materials.
If you have any additional questions, feel free to call the office. We would be glad to help.
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