Knowledge Management is a critical factor for companies worried about increasing their competitive advantage. Because of this, companies are acquiring knowledge management tools that help them manage and reuse their knowledge. One of the mechanisms most commonly used with this goal is that of Knowledge Management Systems. However, sometimes Knowledge Management Systems are not very used by the employees, who consider that the knowledge stored is not very valuable. In order to avoid it, in this paper we propose a three-level multi-agent architecture based on the concept of communities of practice, with the idea of providing the most trustworthy knowledge to each person according to the reputation of the knowledge source. Moreover, a prototype that demostrates the feasibility of our ideas is described.