In order to be certain results we obtain from microbiological/bacteriological testing of a water sample are truly representative of that sample, it is important we take all possible care to avoid contamination of the sample by the bacteria that are all around us – on our skin, in the soil, on the surfaces we touch and sometimes even in the air.
You can help minimise the risk of contamination of your water sample by following the procedures shown below and keeping the following principles in mind:
- collect water samples for microbiological testing only in sterile containers. Laboratory Services will supply sterilised sample containers on request.
- do not rinse out the bottle.
- never touch the neck of the sample container, or the inside of the cap or stopper.
- never put the cap down on any surface and always replace the cap immediately the container has been filled with sample.
- keep the sample container capped until immediately before filling. Avoid breathing, sneezing or coughing over the open sample container, or near the sampling point.
Procedure for collecting samples from a tap
- Run the tap for 2 – 3 minutes (or as long as necessary to flush out the line) before collecting the sample.
- If possible, disinfect the tap by either:
- Sodium Hypochlorite Solution (Liquid pool chlorine, or chlorine based bleaches such as Sno-White are also suitable) - Swab or spray the outside of the tap and as much of the inside as possible with Sodium Hypochlorite solution. Leave for 2 –3 minutes to allow the Sodium Hypochlorite to disinfect the tap. After disinfection, run water from the tap to waste for a sufficient period (at least 1 minute) to ensure that all the Sodium Hypochlorite is removed from the tap before sampling.
- Flaming (suitable for metal taps only, not chrome plated) - Turn off the tap. Flame the tap thoroughly, starting at the nozzle and working back to the body of the tap until the water held in the nozzle boils. After flaming, run water from the tap until it is cool. Be careful not to touch the nozzle of the tap after disinfection.
- Fill the sample container, at a constant flow, taking care to avoid splashing or sample aeration. Fill container to the base of the container neck. Do not overflow the bottle.
Procedure for collecting samples where no tap is available
- Hold the bottle near its base and plunge it, neck downward, below the surface.
- Turn the bottle until the neck points slightly upward and the mouth is directed towards the current. If there is no current, create a current artificially by pushing the bottle forward horizontally in a direction away from the hand.
(NOTE: When sampling from a boat, pontoon etc., samples should be obtained from the upstream side).
Storage and transportation of samples
If samples cannot be delivered to the laboratory within 1 hour of collection, they should be transported to the laboratory in an iced cooler. Ideally samples should be held at 4° (plus or minus 2oC). Samples should not be frozen. Ideally, samples should be delivered to the laboratory within six hours of collection but 24 hours is acceptable, provided the sample has been stored at the appropriate temperature.
Please note that in order to ensure reliable results we need to receive samples for Microbiological testing Monday to Thursday. Samples can not be submitted on Fridays.