Blow-down Water

Water that is drained from cooling equipment to remove mineral build-up is called “blow-down” water or “bleed” water. The cooling equipment that requires blow-down is most often cooling towers, evaporative condensers, evaporative coolers, evaporative cooled air-conditioners, and central boilers (both steam and hot water). These cooling systems rely on water evaporation to garner the cooling effect (latent heat of evaporation). As the water evaporates the mineral content (calcium carbonate, magnesium, sodium, salts, etc) of the remaining water increases in concentration of minerals. If left undiluted, these minerals will cause scaling on equipment surfaces, possibly damaging the system. The blow-down water is usually dumped into the wastewater drain; yet in some cases, this water can be reused for irrigation and other selected uses.