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In spite of the outstanding development of the membranes technology, the "conventional" water potabilization processes are still the large majority worldwide. In any case, both membranes and conventional water treatments rely on the same basic knowledge of the chemistry of the reactions which occur any time a chemical is introduced in a water body. It is significant that 6 out of the 28 parameters listed in Part B (Dangerous chemicals) of the Annex I of the EU Directive 98/83/EC, are likely generated by a poor potabilization treatment or due to an improper selection of materials in contact with drinking water. In addition, even though the Part A of the Directive (Microbial quality) lists only 2 parameters, many other possible pathogens must be monitored depending on the probability of their presence in the water source (protozoa, fungi etc.). Therefore, disinfection plays a fundamental role from both points of view: it keeps the water free from pathogens and their metabolites, while the disinfectant must be selected/dosed/monitored in a way to prevent the formation of dangerous chemicals due to development of reaction by-products. The present handbook is a modest contribution to the knowledge of the above issues and of the chemical disinfection behaviour and specifications. Emphasis is given to the fact that optimum disinfection is made up of an appropriate selection of steps. Each of them must guarantee a foreseeable performance (barrier treatment concept) and the use of disinfectant should be normally delayed as much as possible, that is after other organic and inorganic pollutants have been removed. Fondazione AMGA was established in 2003 to initiate, promote and further cultural initiatives aimed at safeguarding nature and environment, particularly in the field of water resources and water management.