Evaporative coolers, or "swamp coolers," cool the air through water evaporation. One of the biggest maintenance issues facing people who use evaporative coolers is the hard water buildup that occurs on the pads. Removing these deposits is important, because clean pads improve the efficiency of the cooler. Mineral-clogged pads cut down on the amount of water inside the pads and reduce the air flow necessary for creating comfortable indoor temperatures. Softening the water used in your cooler will reduce mineral buildup.
Install an in-line filter for the cooler. These filters remove the dissolved minerals in the water before the water enters the cooler, cutting down on the minerals that can ultimately deposit themselves on the pads. This may be one of the easiest ways to maintain evaporative coolers that sit on roofs, since the filter can be at ground level where it is easier to change.
Add a cap of unscented fabric softener to the cooler once a week, or more frequently during extremely hot, dry weather.
Sprinkle a handful of borax into the water pan in the cooler weekly. The borax softens the water and has no odor.
Add vinegar to the cooler. During the early morning when it's cooler outdoors, put a gallon of vinegar in the cooler pan, then turn off the fan but keep the pump running to dissolve the mineral deposits in the cooler and on the pads. Then, drain the water and refill the cooler with fresh water, turning the fan back on to resume cooling.
Use commercial products designed to reduce the hardness of water in the cooler. This is an alternative to Step 4 if you object to the smell of vinegar. These products are odorless and slightly acidic, which helps counteract the alkaline minerals in the water and dissolve the existing mineral buildup on the pads.