Questions regarding alternative makeup water sources for evaporative cooling have become more prevalent due to water scarcity and water usage concerns. These alternate sources of makeup water can be evaluated if the system is designed to provide consistent makeup water quality to the evaporatively cooled system. The following should be considered during the design please to minimize the potential for adverse impacts in terms of water efficiency or equipment service life. 

Municipal reclaim water quality tends to be more variable compared to city or well water makeup. This variability in water quality can complicate the treatment program for the evaporative cooling system and often requires additional testing and control. Variations in ammonia, bacteria, chloride, fungi, organic and oxidant lo9ading, and phosphate should be planned for and controlled. 

Rainwater harvesting may be appropriate to reduce potable water usage provided the system is designed to capture rainwater and blend it into the makeup in a controlled manner. In addition to storage tank capacity, these systems often require supplemental controls for consistent blending with potable water, filtration to reduce total suspended solids, metering, microbiological control and/or testing, and supplemental pumping. A professionally designed system is more complicated than simply dumping rainwater into the cooling system when it is available. 

Water softeners are sometimes considered to reduce calcium and magnesium hardness to increase water efficiency (cycles of concentration). When considered, the water required to regenerate the softeners should be included in the preliminary analysis. Split-stream sodium zeolite softening may be a cost-effective way to reduce scaling potential. EVAPCO® does not recommend the use of 100% softened water for evaporative cooled systems. Equipment manufacturers, including EVAPCO, suggest that the cooling water have at least 30- to 50 ppm of calcium hardness (as CaCO3) to protect the cooling equipment. If split-stream sodium zeolite softeners are utilized, the treatment program should be cautious in terms of cycled alkalinity, chloride and pH in the cooling water. 

While alternative water sources can enhance sustainability, their use does not offer a ‘free lunch’. A careful analysis should be undertaken to understand the requirements in terms of treatment feed and control, supplemental equipment, and additional testing associated with implementing the use of alternate water for makeup to evaporative cooled systems. The treatment program should detail how the system will mitigate additional corrosion, microbiological growth, operational variability and scaling potential associated with non-potable water use. Please refer to your manufacturers’ IOM for water quality guidelines and recommendations when considering alternative makeup water sources.