Sampling method of water for microbiology testing
Materials and methods:
- 1. Alcohol wipes
- 2. Cooler with gel ice packs
- 3. Rubber gloves
- 4. Water resistant marker
- 5. Sterile sample containers with sodium thiosulfate or as necessary
Samples must be taken from locations that are representative of the water source, treatment plant, storage facilities, distribution network, and points of use. In selecting sampling points, each locality should be considered individually; however, the following general criteria are usually applicable:
- Sampling points should be selected such that the samples taken are representative of the different sources from which water enters the system.
- These points should include those that yield samples representative of the conditions at the most unfavorable sources or places in the supply system, particularly points of possible contamination such as unprotected sources, loops, reservoirs, low-pressure zones, ends of the system, etc.
- Sampling points should be uniformly distributed throughout a piped distribution system, taking population distribution into account; the number of sampling points should be proportional to the number of links or branches.
- The points chosen should generally yield samples that are representative of the system as a whole and of its main components.
- Sampling points should be located in such a way that water can be sampled from reserve tanks and reservoirs, etc.
- There should be at least one sampling point directly after the clean-water outlet from each treatment plant.
A 1 litre sample in a sterilized plastic bottle is required for this analysis (sterilized bottles are provided by the laboratory on request).
Label each bottle with the Client name, Location, Date and Time before proceeding to the site of sample collection.
- When sampling from a tap, first check if there are any leaks from the tap.
- Then open fully and let water run to waste for 2-3 minutes or for a time sufficient to permit clearing of the service line.
- Reduce the flow to permit filling the bottle without splashing. If tap cleanliness is questionable apply a solution of Sodium Hypochlorite (100 mg/L) or flame the faucet before sampling. Let water run for an additional 2-3 minutes after treatment.
- If sampling from a hot/cold tap, run hot water for 2 minutes then cold water for 2-3 minutes and collect samples as above.
- Tightly cap the bottle.
Reservoirs (e.g. Tanks)
- Hold the closed bottle near its base and plunge it below the surface.
- Remove the top and turn the bottle until its neck points slightly upward and mouth is directed toward the current. If there is no current, create one by pushing the bottle forward away from the hand.
- Replace cap before pulling the sample out.
- Tightly cap the bottle.
NOTE: Do's and don'ts
- Do not open the sample container until just before taking the water sample.
- Do not rinse the sample bottle prior to sampling.
- Do collect samples for microbiological examination in sterile containers. The cap of the bottle should not be placed lid down at any point neither should fingers come into contact with the underside of the lid.
- If sampling open tanks, rivers, reservoirs or other sources that require dipping the container into the source, sterilise the outside of the bottles first.
- Do use a new pair of rubber gloves for each sample.
- It is helpful to leave a small air space in the bottle to facilitate mixing by shaking before examination.
- Deliver the sample to the lab within 24 Hrs for analysis.
For more information please contact us through:
Crop Nutrition Laboratory Services Ltd.
Off Limuru Road, Limuru, Kenya
Telephone +254 (0) 711094444, + 254 (0) 720 839 933