This dissertation aims to offer a better understanding of the way Croatian Adriatic, which roughly includes today's Istria, Kvarner, and Dalmatia, including islands, was supplied with water in Roman times. The term "Croatian Adriatic", as defined by J. Riđanović and Z. Bičanić, implies: "...the area of the coastal sea from the middle of the Piran Bay (the mouth of the Dragonja River) in the northwest to Cape Oštri, more precisely in the middle of the outer part of the Boka Kotorska Bay in the southeast, with a 21.2 km long break near Neum. The Croatian Adriatic, in addition to the sea, also includes the areas of municipalities and cities, which, according to the new territorial structure, as units of local administration and self-government, go directly to the Adriatic Sea". An insight into the topic begins with an overview of the geographical features of this area, which is largely characterized by karst relief, rare surface water, and uneven amounts of precipitation. Although sufficient water supply was the basis for quality urban life even in Roman times, which has long been understood, the topic of how sites were supplied with water in the area of the Croatian Adriatic is rarely given enough attention. The scholarly literature that provides an overview of technologies and water supply infrastructure in Roman times is respectable, but not vast. The first investigations of individual water supply systems and parts of infrastructure on the Croatian Adriatic began at the end of the 19th and the beginning of the 20th century, and G. Alačević, L. Jelić, F. Bulić, and A. Gnirs were among the first to deal with them. Professional study of the remains of ancient water supply systems and their parts in the area of the Croatian Adriatic began roughly at the same time as elsewhere in Europe but continued with uneven intensity. In this paper, we provide a brief overview of relevant works on water supply systems from Istria in the north to Cavtat in the south. Therefore, when researching this topic, we collected all the information available to us about the ancient water supply infrastructure. This includes examining how these objects could have been built and for what purpose. When planning and developing water supply systems on the Croatian Adriatic, the ancient engineers encountered various cultural and geographical challenges to which they had to adapt in order to ensure a safer life for Roman colonizers and the population. Help in understanding the technology and the way water supply functioned is also provided by ancient sources. Although several ancient writers touch on the topic of water in their works, which is natural considering its inevitability when thinking about human life and its activities, among the literary sources known to us today only two stand out that paid more attention to water and water supply. For this reason, this dissertation offers insight into the problems, concepts, and basic terms of water supply. When looking at the problem of searching for surface springs, which from the earliest communities were the most important supply points, we rely primarily on historical sources, especially Vitruvius. While considering water quality, we also consider ways of using undrinkable or healing waters, most of which could have been used for various purposes. The dissertation pays closer attention to the issue of technology and considers the ancient technologies necessary for exploiting underground water, rainfall, and spring. Dams were used to protect threatened areas from the destructive effects of surface water, but they also could have ensured a better supply of water in drier periods. We deal with the topic of ancient dams with an overview of general types of dams, which are divided according to the way they resisted the pressure of water. Underground water was mostly accessed by a well or a qanat. Wells are shafts used to dig into the aquifer, and qanats are a type of gravity channel aqueduct that is constructed as an underground tunnel with several access shafts. Rainfall was collected and stored in cisterns. Ancient cisterns were dug into the rock or built of stone or brick and coated from the inside with waterproof plaster (opus signinum), which was made with a mixture of plaster with pieces of ceramic or ceramic powder. In this paper, we have divided aqueducts according to the way they transport water - into gravity channel aqueducts and pressurized aqueducts. The gravity channel aqueducts use only gravity for the transfer of water. On the other hand, pressurized aqueducts in antiquity were usually inverted siphons, which work on the principle of communicating vessels. To the overview of the technology, the topic of mechanisms for raising water is added, which includes various machines and techniques. They form a very important element of some water supply systems, enabling the raising of larger quantities of water with less time or energy consumption, which can facilitate daily supply for the population, as well as simplify the construction of the rest of the infrastructure. Water supply systems, whether for private or public purposes, consisted of a combination of the solutions listed here, which we consider in more detail in the paper. To offer a broader context to the material present in the field, we have offered a summary of the social and legal context that has, equally, shaped the supply. Based on the available information, we have presented the Roman relationship to water and the position of water in Roman law. For this reason, the paper touches on the Roman legal system and how Roman society managed water resources. We concluded that for the Romans, water was a property that could be both privately and publicly owned. This had a special effect on the dynamics of supply. Thus, in its own way, the ownership of springs dictated the need for infrastructure and different solutions in construction. The owner of the land where the spring was located had private ownership of the water source, while water was considered public property if it sprung or flowed on public land. This paper also touches on the question of the legal status of the city's water supply infrastructure, the ways they were financed, and ways of managing them. The city's water supply infrastructure, i.e. the facilities that made it up, also was considered public property, but was not open to everyone and was managed by city magistrates and public authorities. After establishing a basis for our research in this way, based on the already mentioned aspects of water supply - geographical, social, legal, religious, and technological - this dissertation follows an overview of the preserved remains of the ancient water supply infrastructure, as well as relevant data for this topic, derived from previous archaeological research of water supply infrastructure on the Croatian Adriatic. This part of the research is divided into 4 different subparts: a review of the water supply of cities of the Croatian Adriatic, a review of the water supply of rural areas of the Croatian Adriatic, a review of the water supply of the Roman military camps of the Croatian Adriatic and, finally, a review of the issue of the number of ancient cisterns found in the observed area. When reviewing the water supply of the ancient cities of the Croatian Adriatic, we studied the known finds from the area of ancient Poreč, Pula, Omišalj, Rab, Zadar, Caska, Novalja, Nin, Solin, Diocletian's Palace, and Cavtat. When considering rural water supply, we paid attention to the similarities and differences in needs and solutions between urban and rural water supply, and we took the water supply of the famous ancient villa in Verige bay as an example. When reviewing the water supply of the Roman military camps, we concentrated on the review and analysis of finds related to the legionary camps Burnum and Tilurium. We approached the issue of the number of cisterns in the observed area through an overview of known sites with documented cisterns and an analysis of the various uses cisterns could have had and their importance for water supply. According to the available material and knowledge, we believe that cisterns should be distinguished as, primarily, facilities for the storage or distribution of water. In conclusion, the synthesis of available archaeological finds and other data and their analysis created a clearer and refreshed picture of water supply in Roman urban and rural life in this strategic and highly urbanized area of the Roman state.