Changing Concepts of Water Quality

increasing desires or demands of life. Sometimes these concepts change slowly, as exemplified by certain religipns^ or rapidly, as demonstrated by mass hysteria in wars and riots, but change they must. Often changes in concepts are so gradual and subtle that they are not recognized soon enough by the proper authorities. Like all concepts, those relating to the physical, chemical, and biological qualities of water are subject to modification. The public water supply profession is obliged to recognize these changes, to assess them properly, and to determine how they may affect the planning, design, and operation of water works. Failure to do so