Handling and Collection of Water Samples:

The value of any laboratory analysis and test depends upon the method of sampling. Failure to observe proper precautions in securing a representative sample may result in an analysis which may unnecessarily reject a good water supply or more frequently it may certify bad water as satisfactory.

In general, the shorter the time that elapses between collection of a sample and its analysis, the more reliable will be the results. For certain constituents and physical characteristics immediate analysis in the field is required in order to get realistic results, as the composition of the same may change before it arrives at the laboratory. The time elapsed between collection and analysis of the sample depends upon the character of the sample, the particular analysis and the conditions of storage. The time elapsed between collection and analysis should be recorded in the laboratory report.

The laboratory report should also mention if any preservative was added to the sample. If so, name of the preservative should be mentioned. Temperature can change very quickly, pH may change significantly in minutes, and dissolved gases may be lost (e.g. oxygen, carbon dioxide, hydrogen sulphide, chlorine) or gained (e.g. oxygen, carbon dioxide). Therefore, determinations of temperature, pH and dissolved gases should always be carried out in the field. With change in pH, alkalinity and carbon dioxide balance, calcium carbonate may precipitate and this may cause a decrease in the values of calcium and total hardness. Iron and manganese form readily soluble compounds in their lower valence states and relatively insoluble compounds in their higher (oxidized) valence states. Hence, these may precipitate out, or may dissolve out of sediment depending upon the redox potential of the sample.