With the reconstructed and upgraded system for collecting and purifying wastewater on the Krk Island, the aim is to encompass all wastewater whose physical, biological, and chemical compositions have been altered through use. Wastewater includes all potentially contaminated technological, household, rainwater, and other waters. They also participate in the hydrological cycle, where after use, they are conveyed through the sewage system for treatment, i.e., purification, and then returned to the natural environment (recipient). As part of the mentioned project, total investments of approximately 85 million euros are planned to bring the existing wastewater treatment system to satisfactory European standards. The project is co-financed from European Union funds under the Operational Program for "Competitiveness and Cohesion 2014-2020." Given the highly permeable karst terrain and the presence of nearly 20,000 inhabitants in 68 populated areas, wastewater management is of utmost importance, particularly from an ecological standpoint. The current drainage of wastewater and rainwater from residential and commercial zones has not met the criteria of modern technology. The existing state of the public wastewater and rainwater drainage system on the Krk Island has been developed under the concept of one settlement- one system, resulting in seven different public wastewater drainage systems. The aim of this thesis is to consider the unification of the existing systems into a single system and to increase the control over purification and its quality. The paper will present proposed drainage solutions and new wastewater treatment technologies that are part of the mentioned project.