How do we measure water quality?
To identify the substances present in a stream or lake, scientists collect samples of the water, of living organisms, and of suspended and bottom sediments. Technicians then analyze these samples in a laboratory with specialized instruments and procedures. Certain measurements such as temperature, dissolved oxygen, turbidity and conductivity can be taken in the field with portable equipment.
Today's analytical laboratory instruments – with such high-tech names as "plasma emission spectrometer" (for analysing metals) and "gas chromatograph-mass spectrometer" (for analysing pesticides, PCBs dioxins, and other organic compounds) – bear little resemblance to the test-tube and gas burner laboratories of the 1950s.
Nowadays the analysis of water and sediment samples detects more substances than a decade ago, partly because there are more substances present in water, but also because of improved analytical instruments and consequently lower detection limits. State-of-the-art analytical instruments can detect down to one part per trillion of some substances – comparable to tracing one thousandth of a teaspoon of salt dissolved in an olympic-size swimming pool.
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