# Cycle of Concentration

A cycle related to the changing ratio of solids and water volume in any vessel from which water evaporates, such as a still, a swimming pool, a steam boiler, or a cooling tower. As the water evaporates, the formerly dissolved solids remain behind. The new water which is added (to replace the evaporated water) also contains dissolved solids, so the concentration ratio of solids to water increases proportionately. For example: assume a boiler system holds a total 1,000 gallons of water. When the first 1,000 gallons evaporates, the solids are left behind. Then an additional 1,000 gallons of makeup water is added (to replace the evaporated water) and the makeup water also contains a quantity of solids. The system still holds only 1,000 gallons but the amount of solids has now doubled and the system now holds two concentrations of solids. The concentration is now two (solids) to one (volume of water). If 3,000 gallons of makeup water are added, the concentration becomes four (solids) to one (volume of water). These calculations of concentration ratios are used to determine when blowdown is needed in boiler or cooling tower operation.