The methods of analysis presented in this work as ¿Principles and Practices of Spectrophotometer¿ are believed to represent the best current practice of the laboratories and research sector of Cairo water company, and to be generally applicable in connection with the ordinary problems of water quality measurements. Part I, underwent a scope on the principles of the spectroscopy, Beer's law and the deviation caused, expression used and the differences between single and double beam spectrophotometers. Part II, dealing with the measuring modes and how the light fare interacts with matter. Part III, was clarifying the types of tools, glass, and plastic wares used.