The sewage plant will stop pumping out sewage if its power is gone. The sewage that floods the power plant will then drain away; it is only flooded if there is

The sewage plant will stop pumping out sewage if its power is gone. The sewage that floods the power plant will then drain away; it is only flooded if there is a continuous influx of sewage. So yes, it looks like this is a proper NOT gate because the power plant is flooded iff the sewage plant's power is on (modulo propagation delays).