Water sampling

WATER SAMPLING PROCEDURES

Wrong sampling procedures and methods will affect the accuracy and reliability of analytical results and lead to misleading conclusions on the quality of the water supply.

A representative water sample can be described as a sample that meets the objectives of sampling, and that has been collected at a place that truly represents the water at the point of concern in the water supply system.

Do not sample from the tank and do not sample after the filtering system, unless you want to test the filtered water. Sample directly from the source.

Borehole and Municipal Water sampling:

• Keep sample bottles closed until they are to be filled.
• Please use any good plastic bottle, preferably a bought mineral or water bottle, already sterilised/cleaned. (NO Glass, Milk or Fruit juice bottles please). Where sterile bottles are not available, representative microbiological samples can still be collected by rinsing bottles with hot water, followed by the sample.
• Take the water sample directly from the water source you would like to test. Let the water run for 5 to 10 minutes.
• Remove the cap of bottle and ensure no contamination of cap or the neck of the bottle when filling occurs. Rinse the bottle thoroughly with the source water and fill to the neck of the bottle. Never sample leaking taps, where water runs down on the outside of the tap.
• Close the lid tightly and test bottle for any leaks. Please supply 2 x 1 litre bottles per borehole/source, as this expedite the test results. Keep the water samples in the dark, and keep them cool until the couriers arrive.
• Although recommendations vary, the time between sample collection and analysis should, in general, not exceed 72 hours, and 72 hours is considered the absolute maximum. It is assumed that the samples are immediately placed in a lightproof insulated box. Sample temperature should be kept below 100˚C for a maximum transportation time of 48 hours.

Waste/Effluent Water sampling:

Wastewater sampling is generally performed by one of two methods, grab sampling or composite sampling.

Grab sampling is just what it sounds like; all of the test material is collected at one time.  As such, a grab sample reflects performance only at the point in time that the sample was collected, and then only if the sample was properly collected.

Composite sampling consists of a collection of numerous individual discrete samples taken at regular intervals over a period of time, usually 24 hours.  The material being sampled is collected in a common container over the sampling period.  The analysis of this material, collected over a period of time, will therefore represent the average performance of a wastewater treatment plant during the collection period.

• Rinse the clean sampling device in the wastewater.
• Take the sample using the sampling device, scooping in the direction of the flow.
• Pour carefully into the clean, labelled sample bottle.
• Repeat until the sample bottle is filled to the brim and close the lid tightly.
• Avoid contaminating the outside of the bottle.
• Spray down the sample bottle with 70% v/v ethanol and wipe down with a paper towel.
• Place the sample bottle on ice, in the cooler box.
• Rinse the sampling device with water and spray down with 70% v/v ethanol and let air dry.