For several years, the management of water passing through the cities (stormwater, waste water, drinking water, water for leisure, etc.) has changed considerably in order to meet a variety of issues (use of water in the city, protecting aquatic environments, protection against floods, etc.). The multiplicity of actors, at various territorial levels, adds to the complexity of management. Thus, the Omega multi-group research (ANR Sustainable Cities 2009) proposes a method for evaluating issues of the urban water management system, also called service’s functions (an action expected of a product (or carried by it) to respond to an element of a given user need), by creating interaction and cooperation between all stakeholders. On the complex site of Bordeaux’s lake, four service’s functions (“to control the cost of the system”, “to preserve the aquatic environment”, “to respect uses of the aquatic environment” and “to value urban water for urban life”) have been evaluated and crossed to identify actions to improve the system. The assessment requires the definition of understandable indicators for each function; such as the attendance of users or the loss of perch. Each indicator was then measured and adjusted to a value scale before coming to a dashboard for the study site. Although the attendance remains correct, the users’ satisfaction about environment is average; green spaces seem insufficient and the aquatic environment seems degraded with a limited presence of perch and a number of swimming areas’s closuring days too high. Finally, the functions were crossed by identifying common sources limiting and proposing remedial actions. Discharges stormwater and wastewater, the urbanization of the site and unfriendly practices are common sources for different functions.