One of the most important input providers for data stream management systems (DSMSs) is a sensor network. Such a network can have query functionality offered as a sensor network query processor (SNQP). Then some of the data stream operators can be executed in the DSMS as well as in the SNQP. This paper addresses the problem of finding the optimal solution. It shows first steps like the moving of operators and the modification of the epoch duration. The primary goal is to prolong the lifetime of the sensor network. A QoS-based goal function is introduced, and the optimization process is explained. It has been implemented with Borealis and TinyDB. Some preliminary results from the ongoing evaluation are given.