Evaporative cooling is highly dependent on your climate – on your region’s temperature and humidity. In drier, hotter climates, the unit will use more water. And, of course, if you choose a higher speed fan setting, then more water will be used too. On average, the water tank lasts around 6-8 hours during the hotter day hours – and 8 – 10 hours during the cooler nights. Once the water tank empties, a low water alarm beeps, an indicator light turns on, and the unit will continue fanning but not cooling.