"When considering the treatment of various water supplies, we usually focus our attention on the major constituents, such as calcium, magnesium, sodium, alkalinity, chloride, and sulfate. However, a closer examination of water treatment practices reveals that it is frequently the minor components which represent the controlling factors in many situations. For example, traces of organic matter (chlorotorm), viruses, fluorides, and silica sometime determine the overall design of the water treatment system. These constituents may be present in concentrations as low as parts per billion, or a few parts per million, but their importance can rival that of other components present at much higher concentrations. This issue of Amber-hi-lites will be devoted to one of these minor components, silica."