TRD: Institute for Plant Production: Laboratory Services: SOIL, WATER AND PLANT TISSUE LAB
Water sampling
Samples should be collected in clean, plastic bottles that have been rinsed three times prior to use. For the purpose of irrigation analysis, fill the container. Well-water samples should be collected after pumping for at least 30 minutes. Sampling from distribution systems should be done after the lines have been flushed sufficiently to ensure that the sample is representative of the supply.
Representative samples of some sources can only be obtained by making composite samples collected over a period of time or at many different sampling points, but sometimes it is more informative to analyse numerous separate samples.
When samples are collected from a river or stream, results may vary with depth, stream flow, the distance from the shore, and from one shore to the other. Lakes and reservoirs are subject to considerable variations due to natural causes such as seasonal stratification, rainfall, run-off and wind. Avoid surface scum or collecting at weirs. Generally, collect samples beneath the surface in quiescent areas.
If NO3-N is an element of interest and the analysis cannot be completed within three hours of collection, the samples should be frozen or kept below 4°C. Samples collected for alkalinity, conductivity, phosphate and sulphate should also be refrigerated until analysis can be completed. If micronutrients are of interest, the sample, or a sub-sample, should be acidified to pH < 2 as soon as possible after collection due to the problems of absorption or precipitation.
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