An evaporative chiller cooling water to below ambient wet bulb temperature. Sub-wet bulb chilling is achieved by pre-cooling incoming air upstream of the saturator. The incoming air is ambient air at ambient air temperature that is cooled using the coolness of the lower temperature outgoing air exiting the saturator. The pre-cooling lowers the temperature of the incoming air and lowers its wet bulb temperature below that of ambient air. The saturator water is chilled to below the ambient wet bulb temperature. The air in the saturator flows across the water as it gravity drips or flows from the top to the bottom of the saturator. The pre-cooled air flows across the saturator with the coolest air directed across the bottom of the saturator where the coldest water is flowing and with the hottest air directed across the top where the hottest water is flowing to provide gradient chilling.