Evaporative coolers are common in low humidity regions due to their lower purchase and operating cost when compared with reverse cycle air-conditioning. These units do consume significant volumes of water and the amount of water consumed increases both with hours of use as well as due to poor maintenance and cleaning.
Water is used in two ways with evaporative cooling. The cooling effect is a result of water being evaporated into air that is flowing into the home. Excess water that isn’t evaporated is recirculated several times via a sump and pump system.
Evaporation only removes pure H20 and leaves behind any salts or minerals present in the water supply. To manage the salt concentration in the sump, the evaporative cooler will use one of several options to dump the salty water to drain and top-up the sump with fresh water. This process is the second way that an evaporative cooler uses water.
Most larger evaporative coolers are located on the roof and this makes routine maintenance a challenging task that is best undertaken by a trained technician using adequate tools and safety equipment.
Evaporative coolers will use between 25.5 and 40 litres / water per hour when running efficiently. Water hardness, a build-up of salts and minerals and accumulated dust in the evaporative pads will reduce the cooling effect dramatically and result in higher fan speeds or longer running time to achieve the desired cooling effect.
A real-world study undertaken by Yarra Valley Water in 2005 found that water use varied from 10L / minute to less than 0.5L /min. Daily usage ranged from 81 to 305 Litres / day.