The need for safe, healthy water is critical to all human life. The search for ways to ensure a ready supply of high quality water has been the life's work of some of our brightest scientists, and the amount of technical knowledge they have generated can fill volumes of text. Such a vast amount of knowledge is beyond the scope of this manual. Our need for knowledge of water quality issues is more practical, more job and customer oriented. We have therefore, made a serious effort to limit this manual to 'purposeful information.'