Featured Application: The research results have direct practical applicability. The research topic was generated by designing the water supply network of the city with 300,000 inhabitants. The results obtained and the proposed solutions can be applied to similar water supply networks, the practical importance being significant if we consider that all the cities that are found in the modern world possesses water supply networks.Abstract: This paper studies the mechanical behavior of high-density polyethylene (HDPE), from which the pipes used for water transport in water supply networks are manufactured. The study was generated by the practical problem of replacing and modernizing a water network of a city with 300,000 inhabitants. Of the numerous problems that have arisen and been solved by the group of researchers, only those referring to the mechanical behavior of the materials used for pipes are presented. HDPE, which is a thermoplastic material, is suitable for manufacturing the pipes used in water supply networks, having many advantages. Data on the mechanical properties of the material of which the pipe and elbow are made is obtained experimentally. The work involved the main steps required to design a water network, but the subject is not exhausted. The stresses in the polyethylene pipe are determined in two cases: buried in the ground and supported in a concrete massif. Thus, by calculation, the advantage offered by the second solution is justified. The crack of the pipes manufactured from HDPE is studied, taking into account the classical model used in the cracking process. A simulation of pipes and elbows cracking was made. The results obtained via MEF are useful for the users of the networks.The pipe, as the main element of a supply network strictly necessary for the transport of water, was made, for more than two millennia, out of traditional materials that were common at the time in those communities where they were used (stone, ceramics, wood, metals, non-metals, etc.). Constructive variants of pipes, of different shapes and sizes and made of different materials, have been used by many and various civilizations that have followed one another throughout history, and countless artifacts can illustrate this development.Water supply networks experienced great development, especially in the second half of the twentieth century when science and technology allowed for the emergence and production of plastics, which became the main materials of the pipes used in water supply networks. The most suitable and current plastic material used to produce the pipes needed for water transport in modern water-supply networks has been proven to be HDPE. The pipes and fittings obtained are characterized by a long service life, low maintenance costs, and their remarkable special strength and low weight. The HDPE pipes have many advantages in comparison to the classic ones used so far. Listing some of them ([2,3]): they allow a long service life; they do not need cathodic protection systems; there is no need for additional...