The atmosphere at typical jetliner cruising altitudes is generally very dry and cold; the outside air pumped into the cabin on a long flight has the potential to cause condensation which might in turn cause corrosion or electrical faults, and is thus eliminated. Consequently, when humid air at lower altitudes is encountered and drawn in, the ECS dries it through the warming and cooling cycle and the water separator mentioned above, so that even with high external relative humidity, inside the cabin it will usually be not much higher than 10% relative humidity.