In this thesis there was description of the development of the model of maintenance of public drainage systems in the Republic of Croatia. Good maintenance of the sewage system is a prerequisite for rational management of expensive urban infrastructure, good sanitary conditions in the urban environment and good environmental protection. Good maintenance of the drainage system is one of the prerequisites for sustainable development and a healthy standard of some urban environment, so it has to be given great attention. Good quality water management in the Republic of Croatia is maintained as a unique and irreplaceable natural resource with a limited amount of water. The development of a model for the maintenance of public drainage systems in the Republic of Croatia has been described for achieving the mentioned goals in this thesis. The model must fit into the existing state and at the same time offer a viable way of improving the existing state, relying on existing available resources. For the implementation of the new model, it is necessary to purchase new equipment or software. The model must offer and ensure the improvement of the existing situation in maintaining the drainage system in the Republic of Croatia. The documented existing practice in municipal utility companies needs to be improved with mathematical models and appropriate CCTV camera equipment and maintenance of drainage systems (special high pressure and vacuum cleaners, robotic barrier and damage elimination systems, local rehabilitation equipment etc.) Based on an objective assessment of the state of the system, it is possible to plan the necessary resources (financial, personnel, technical) and timely coordinate system maintenance activities, all in order to meet the applicable legal regulations and set environmental objectives. With the assessment of drainage system status according to the model, expert and scientifically based backgrounds for planning and carrying out maintenance activities and rational spending of all the required resources are obtained.