How To Collect A Sample

“The result of any testing method can be no better than the sample on which it is performed.”

That being said, the objective of your sampling would be to collect a sample volume small enough to be transported conveniently, but large enough for analytical purposes while still accurately representing the body of water being sampled.

   General requirements:

Handle samples so they do not deteriorate or become contaminated before testing. Sample carefully to ensure analytical requirements represent the actual sample composition.

The choice of sample bottles should be influenced directly by the analyses required. Samples for trace metals should not be collected in sample bottles with metal components.

Avoid using plastic bottles when sampling for organics as plasticizers may leach and contaminate the sample. Microbiological sample bottles should be sterile.

All sample bottles should be clearly marked in detail with the sample identification, sampling date, sampling time, origin of the sample and type of sample (drinking, waste, etc).

Keep samples as cool as possible between sampling and analysis. Do not freeze samples! A temperature of approximately 10 °C is optimum. Preferably pack water in crushed or cubed ice during transportation.


   Microbiological samples:

(Fecal coliforms, Total Coliforms, E.coli, Heterotrophic Plate Count)

Microbiological samples should be collected in sterile glass or plastic bottles. If no sterile bottle is available rinse bottles with boiling water followed by the sample after flushing the distribution line.

Take care not to contaminate the bottle or cap.

Once the distribution line is flushed, open the cap holding it by its outside edges only and fill sample bottle.

Cap sample and place in a cooler with ice.

Holding times for Microbiological samples are minimal (6 hours). Deliver samples to the laboratory as soon as possible after sampling.

Sample volumes of 250mL will be sufficient to complete all routine Microbiological analyses.


   Samples for Chemical Analyses:

Potable Water

(Any water source that can be used as drinking water)

Keep sample bottles closed until they are to be filled.

Be selective of sampling points – do not sample from leaking taps where water has been allowed to run down on the outside of the tap.

Flush tap by running the water before collecting sample.

When collecting water samples from wells and boreholes pump water for approximately 5 minutes before a sample is collected.

When sample locations for a distribution system are identified include dead-end sections and all the different lines in the sample programme.

A sample volume of 750 mL is generally required for drinking/potable water dependent on drinking water package selected.


Waste/Effluent Water:

(wastewater – either treated or untreated – that flows out of treatment plants, sewers or from industrial processes)

Where possible collect waste/effluent water samples directly in the sampling bottle. If not possible, a pre-rinsed jug/beaker can be used to fill the sampling bottle.

Holding the sampling bottle near its base plunge it mouth downward below the surface of the water – particularly when sampling from a dam. Never sample water from the surface.

Sampling frequency of wastewater may be seasonal for recreational waters, daily for water supply intakes and hourly for wastewater where the quality of the water may vary significantly.

Irrigation waters require a sample volume of 750mL, whereas, dependent on the package effluent water sample volumes range from 250 mL for IPW to 500 mL for River Disposal.


 Sample preservation and storage:

Not only are holding times important for microbiological samples, but various chemical parameters such as acidity and alkalinity also have short holding times. It is assumed that the samples are immediately placed in a lightproof insulated box containing melting icepacks with water to ensure rapid cooling. Sample temperatures should be kept below 10°C for a maximum transportation time of 6 hours. If ice is not available transportation times must not exceed 2 hours.