(at around 1h 8 mins) If the microwave emitter really evaporates all water in the vicinity, in theory it should also kill everyone standing near it, as human bodies consist mostly of water. However, it is mentioned earlier in the film that the emitter uses "focused microwaves" specifically designed to target an enemy's water supply. For the safety of those operating it, the device was presumably designed only to affect water at certain levels of pressure.