Moderni urbani vodoopskrbni sustavi zahtijevaju energetsku i hidrauličku održivost. U posljednje vrijeme teži se korištenju obnovljivih izvora energije, a naročito solarne fotonaponske energije u svrhu proizvodnje električne enegije za rad navedenih sustava. Korištenje solarnih fotonaponskih (FN) ćelija u svrhu proizvodnje električne energije za rad crpnih stanica, koje crpe vodu, je već dobro poznata i uhodana tehnologija. U pravilu se takvi sustavi sastoje od FN generatora, crpne stanice i vodospreme. Dosad su se za dimenzioniranje urbanih vodoopskrbnih sustava pokretanih FN energijom koristili pojednostavljeni postupci i metodologije koji su djelomično rješavali problem pouzdanosti i učinkovitosti vodoopskrbnih sustava. U ovom je radu prikazana i opisana Metoda kritičnog perioda (MKP), osmišljena upravo u tu svrhu, čime je napravljen matematički model kojim se dimenzioniraju energetski održivi urbani vodoopskrbni sustavi (EOUVS). Pri tome su razmatrana dva načina formiranja ulaznih i izlaznih vremenskih serija svih veličina potrebnih za proračun. Nadalje, analizirane su funkcionalne zavisnosti veličina pojedinih dijelova urbanog vodoopskrbnog sustava dimenzioniranog takvom metodom, pri čemu se utvrdilo da između pojedinih dijelova postoji funkcionalna povezanost. Time se dobio detaljniji uvid u rad takvog sustava..; Modern urban water supply systems require energy sustainability as well as hydraulic sustainability. In recent times, efforts have been made to use renewable energy sources, particularly solar photovoltaic energy for the electrical power generation necessary for the operation of these systems. The use of solar photovoltaic (PV) cells for electricity production needed to operate water pumping stations is already a well-known, established technology. Such systems typically consist of a PV generator, pumping station and water tank. To date, the dimensioning of urban water supply systems operated with PV energy have utilized simplified procedures and methodologies which partially solved the problem of reliability and efficiency of these water supply systems. The paper presents and describes the Critical Period Method (CPM) designed for this purpose, which has devised a mathematical model for dimensioning energy sustainable urban water supply systems (ESUWSS). In doing so, two manners of forming input and output time series of all sizes necessary for the calculation were considered. Additionally, functional dependencies of the sizes of individual parts of urban water supply systems dimensioned by the application of this method were analysed. It has been determined that there is a functional dependency between the individual parts, thus providing a better insight into the operation of such systems.