A laboratory doing trace element analysis has a need for water of extremely high purity, e g for preparing calibration standards with low and well-controlled concentrations. Ordinary tap water contains considerable amounts of many substances and is thus unsuitable in most applications in the laboratory. It is therefore purified in several steps, resulting in different levels of purity:

1. De-ionized water (conductivity not exceeding 10µScm-1). Tap water is first filtered, then purified by ion exchange in Seradest LFM 20 systems. This water is mainly used for cleaning of labware. Part of this water is further purified in step 2.

2. "Milli-Q" water. Water from step 1 is cleaned by carbon adsorption and ion exchange (System: Millipore Milli-Q). Widely used in the laboratory for diluting samples, preparing solutions etc. This water is controlled by ICP-SFMS screening; the concentrations for the elements in package V-2, including its supplementary elements, must then lie below reporting limits. This water is further purified in step 3.