3 – Sampling and analysis

Publisher Summary To obtain an accurate representation of the composition and nature of a water or wastewater, it is first essential to ensure that the sample analyzed is truly representative of the source. Having satisfied this requirement, it is then necessary to carry out the appropriate analytical procedures using standard techniques that have been developed specifically for water and wastewater analyses. The collection of a representative sample from a source of uniform quality poses few problems and a single grab sample is satisfactory. A grab sample is also sufficient if the purpose of sampling is simply to provide a spot check to see whether particular limits have been complied with. However, most raw waters and wastewaters are highly variable in both quality and quantity so that a grab sample is unlikely to provide a meaningful picture of the nature of the source. When designing a sampling program, it is vital that the objective of the exercise be clearly specified, for example, to estimate maximum or mean concentrations, to detect changes or trends, to estimate percentiles, or to provide a basis for industrial effluent charges. The degree of uncertainty that can be tolerated in the answer must be specified and it is also necessary to bear in mind the resources available for sampling and analysis.