The first known systems that used water to cool indoor spaces were created by the ancient Egyptians, who lowered the temperature in their homes by hanging wet mats over their doorways. The evaporated water from the wet mats reduced indoor air temperatures and added refreshing moisture to the dry desert air.

Not long after the Egyptians beat the heat with their doorway mats, the Romans developed a primitive air conditioning system by utilizing their famous aqueducts to circulate fresh water through indoor pipes, a method that significantly reduced the air temperature inside stuffy villas.