Volume 5 Issue 1
Katie Odrobina, Senior Consultant, Produce Food Safety
Most operations are aware that they should periodically be testing their water sources at the farm, packing and storage facilities. Not everyone though has been taught how to properly take a water sample. Many laboratories simply send water sample containers and neglect to include instructions. Improperly taking a water sample can lead to false positive or false negative test results.
Sodium Thiosulfate Tabs
Some laboratories provide water sampling containers which contain a small tablet or powder. This substance is sodium thiosulfate which is used to neutralize any residual chlorine present in the water sample. If sodium thiosulfate is present in the sample container it should not be removed when collecting the sample or it should added back to the sample after the water is collected.
How to Take a Sample
The follow are guidelines for how to properly take a water sample based on the requirements of the FDA’s Bacteriological Analytic Manual and the Standard Methods for the Examination of Water and Wastewater.
- Collect materials needed for the sampling – water sample container, alcohol wipe, gloves
- Wash your hands
- Before taking a sample put on a new pair of gloves
- If sampling a closed water systems (facility faucets, well spigots, etc.), disinfect the water tap/spigot with an alcohol wipe. Turn on the water and let it run for at least 3 minutes
- Open the water sample container. Do not touch in the inside of the container. Do not dispose of the sodium thiosulfate tablet (if it is present)
- Fill the container to at least the fill line without allowing the container to overflow. The laboratory needs at least 100 ml of water to perform the test.
- If sampling an open water source (pond, river, canal, etc.), plunge the water sample container into the water source and turn the opening of the container towards the current and allow to fill.
- Tightly cap the water sample container. If there is a security tab or device use it.
- Label each sample individually with at least the water sample source or sample code. If using a sample code make sure to include the key when sending the samples to the laboratory.
- Complete laboratory paperwork for what tests to perform on the sample.
- Place the sample in a cooler/lunch box with gel ice packs (do not use dry ice). Make sure the sample is in contact with the sample container. Add extra padding to make sure that the sample does not roll around in the cooler and stays in contact with the ice pack.
- Transport sample to the laboratory for testing. The laboratory must receive the sample within 24-30 hours after the sample is taken for the results to be valid.
Special Notes on Testing Ice
Ice is considered to be a type of water and should also be tested if it is being used in the process or for shipment.
To perform the test, the laboratory still needs at least 100 ml of water. If 100 ml of ice is collected it will not equate to 100 ml of water once it has melted. Allow the ice to melt before filling the water sample container.
For more information, questions or consulting services please contact Katie Odrobina directly at 706-881-0092, kodrobina@producefoodsafetyservices.com or visit the website at www.producefoodsafetyservices.com.