The paper tackles an issue that concerns both the suppliers and consumers of electric energy: power losses in distribution power networks. On the other hand, the harmonic pollution in power networks has become a permanent issue, and in many situations along with the unbalance determines a steady state that is unbalanced and non-sinusoidal. In the design and exploitation stage the power engineers calculate the power losses considering the ideal case (sinusoidal and balanced), approach that brings many disadvantages. Thus, the authors propose a methodology for power losses calculus that take in consideration the existence of unbalance and harmonic pollution. The suggested method implies the use of the power quality indices that characterize the real steady state.