In this paper, we explore some aspects regarding the introduction of an active learning approach to deal with environmental issues in secondary school during natural sciences lessons. Integrated curricular program and PBL (problem-based learning) are comprehensive approaches designed to engage students in investigation of authentic problems. We used a scenario regarding water as a socio-environmental issue to introduce the hydrosphere curricular topic. Two different ways were used for the presentation of the scenario. Here, we present students' and teachers' perceptions about the PBL approach, as well as students' ideas about water proposed in both cases. Discussion among students was more active, when less input was given. Even though some difficulties arose, PBL approach was appreciated by the majority of students and teachers. (Contains 5 tables.) [This paper has been supported by the I+D+i Research Program of the Spanish Ministry of Science and Innovation,]