The Brazilian Ministry of Health proposed a research study involving municipal professional staff conducting both epidemiological and water quality surveillance to facilitate the integration of the data which they collected. It aimed to improve the intersectoral collaboration and health promotion activities in the municipalities, especially regarding drinking-water quality. We then conducted a study using the action-research approach. At its evaluation phase, a technique which we called 'the tree analogy' was applied in order to identify both possibilities and challenges related to the proposed interlinkage. Results showed that integrating the two data collection systems cannot be attained without prior institutional adjustments. It suggests therefore the necessity to unravel issues that go beyond the selection and the interrelation of indicators and compatibility of software, to include political, administrative and personal matters. The evaluation process led those involved to re-think their practice by sharing experiences encountered in everyday practice, and formulating constructive criticisms. All this inevitably unleashes a process of empowerment. From this perspective, we have certainly gathered some fruit from the Tree, but not necessarily the most visible.