Any evaporative cooler that uses a bleed valve to flush a portion of the re-circulating water and/or water from its reservoir produces wastewater. Coolers without a bleed valve use an average of 3.5 gallons per hour, while the coolers with a bleed valve use 10.5 gallons per hour, (Karpiscak et. al. 1998), thus coolers probably generate about 7 gallons of waste water per hour. The wastewater can either be drained to the sanitary sewer system or reused on-site.
Wastewater from an evaporative cooler can be re-used for irrigation purposes. Irrigation is a natural use for this water since the hot, dry conditions that often spur cooler use also spur irrigation demand. However, evaporative coolers also typically function in desert areas where the water has a high concentration of salts. This is a concern for plants that are sensitive to water with a high mineral concentration. In a study conducted by the University of Arizona’s Office of Arid Land Studies, it was found that coolers with a bleed off system produced wastewater with total dissolved solids (TDS) of 375 to 4,043 Mg/L. In general, water with a TDS below 5,000 Mg/L can be used for most irrigation (Karpiscak et. al. 1998). Nevertheless, you may want to research specific plants before irrigating them with the wastewater.
In addition, continual use of your cooler may cause overwatering. This is especially true if you don’t move the bleed-off hose regularly to different areas of your landscape. Alternatively, you can connect the bleed line to an underground irrigation system, such as drip irrigation, as shown below.
Figure 1: An example of a bleed line that connects to drip irrigation. Source: Aquacraft, Inc., by permission.
Karpiscak, M.M., et. al. 1998. Evaporative cooler water use in Phoenix. Journal AWWA, 90(4): 121-130.