Before the miniature nitrate sensors designed by the CENS Embedded Sensor Project can be integrated into a wireless sensor network, each sensor must first have a sample preparation system that filters the incoming ground water for substances that could damage the sensor or cause faulty results, while still preserving the substance to be measured. Therefore, we are designing a compact, low-power system to provide a continuous stream of segregated acceptable samples to the sensors to enable them to work in remote environments.