Many FB datacenters use evaporative cooling systems rather than traditional A/C, basically spraying water into the incoming air supply to cool it below outdoor

Many FB datacenters use evaporative cooling systems rather than traditional A/C, basically spraying water into the incoming air supply to cool it below outdoor ambient temperatures. The hotter it is outside, the more water is needed to cool the air, trading temperature for humidity. But this water can't easily be recaptured without using significantly more energy than normal A/C, so the evaporated water is exhausted as part of the hot air from the DC aisles.