INTRODUCTION This article analyzes electrical and water consumption for four different cooling systems combined with three different humidification systems on hypothetical telco/data centers located at 262 cities throughout the United States. The four analyzed cooling systems include refrigeration only@ refrigeration with dry coolers@ refrigeration with water economizers@ and refrigeration with air economizers. These cooling systems do not represent every conceivable model@ but they do represent the most common configurations. The three analyzed humidifiers include steam@ ultrasonic and evaporative. Equipment@ installation@ and maintenance costs are not directly addressed.