The distribution system is a critical component of every drinking water utility. Its primary function is to provide the required water quantity and quality at a suitable pressure, and failure to do so is a serious system deficiency. Water quality may degrade during distribution because of the way water is treated or not treated before it is distributed, chemical and biological reactions that take place in the water during distribution, reactions between the water and distribution system materials, and contamination from external sources that occurs because of main breaks, leaks coupled with hydraulic transients, and improperly maintained storage facilities, among other things. Furthermore, special problems are posed by the utility’s need to maintain suitable water quality at the consumers tap, and the quality changes that occur in consumers’ plumbing, which is not owned or controlled by the utility.