Potable Water Sample Collection, Transport and Delivery
Around the time of the Havelock North incident, Eurofins-ELS started to examine the full process of collecting drinking water samples from the time the sampler arrives at the sample point until the sample is received at the laboratory. This process is also part of the Havelock North enquiry.
We reviewed other laboratories techniques, and contacted many of our customers to ask them how they sterilise their sample points prior to flushing. We received many different answers with the most common techniques being:
|
Sterilisation of the Tap
We performed dozens of tests using these techniques to work out which is the best. Our test process saw us pouring diluted effluent onto a tap then using a sterilisation technique prior to collecting an E. coli/Total Coliform sample. We discovered that while all techniques apart from ‘flushing only’ reduced the presence of E.coli flaming the tap with a propane burner was the best technique.
However, flaming is not always ideal in the field. Any taps with plastic fittings would be damaged and the risk of setting fire to dry grass or even wooden fittings is always present.
The best second option we found was to use either alcohol wipes or methylated spirits ensuring all parts of the tap are cleaned (inside as well) and with at least 30 seconds contact time.
Flushing the Tap
Once the tap has been cleaned and sterilised we recommend that it be flushed for sufficient time for the mains water to be pulled through. This can vary from site to site and can usually be confirmed by recording a steady chlorine reading or temperature. Most taps require at least 2 minutes.
Transporting the Samples
When carrying the samples around the sample run we recommend using a purpose built holder. Many samples are received at this laboratory rolling around at the bottom of a chilly bin and this can lead to cross contamination from unclean chilly pads or the bin itself.
Eurofins-ELS has designed and built a sample holder (see picture on the right) and we will be sending these to our customers in the coming month. We will include some instructions on the best way to use them.
Temperature control is also very important when transporting samples with the objective of maintaining them at between zero and 10ºC, but not frozen, when they arrive at the laboratory.
Arrival at the Laboratory
When your samples arrive at the lab we will check the temperature and condition of the samples and ensure the correct bottles have been used. If we find any problem we will get in contact with you.
Following the correct process from start to finish will ensure that we deliver the most accurate results, and we will work together to achieve this objective.
