Contaminant, origin system related

Intuitively we can feel that the economical value of the analytical result is related to its quality. The quality of an analytical result depends upon two factors first of all we should know how confident we are about the produced result. In fact, an analytical result without an explicit or implicit (by the number of significant figures) indication of its precision has no quality at all. Second, the quality of the analytical result depends on how well the sample represents the system of its origin. The sample may be contaminated or may be modified because of inappropriate storage and aging. In other instances, when the sample is taken from a chemical reactor in which a chemical reaction is occurring, the constitution of the reactor content is usually time varying. Because of inevitable time delays in the analytical laboratory, the constitution of the sample will not anymore represent the actual constitution in the reactor at the moment when the analytical result is available. Therefore, both the precision of the analytical method and the analysis time are important indicators for the quality of an analytical result . ... 

The quality of water, as true for other commodities, depends on its origin or source, the factors which influence its composition during transport and storage, and on the processes which have been applied to improve its quality. The concerns for quality can, therefore, be source related if the source of water is contaminated, treatment related if the concern stems from the techniques used to treat water, or distribution related if it is the distribution system that is in question. The quality requirements for water depend on its intended use, and the criteria identified for monitoring quality are determined accordingly. 

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