the capacity of the dm plant is dictated by the type and quantity of salts in the raw water input. however, some storage is essential as the dm plant may be down for maintenance. for this purpose, a storage tank is installed from which dm water is continuously withdrawn for boiler make-up. the storage tank for dm water is made from materials not affected by corrosive water, such as pvc. the piping and valves are generally of stainless steel. sometimes, a steam blanketing arrangement or stainless steel doughnut float is provided on top of the water in the tank to avoid contact with air. dm water make-up is generally added at the steam space of the surface condenser (i.e., the vacuum side). this arrangement not only sprays the water but also dm water gets deaerated, with the dissolved gases being removed by a de-aerator through an ejector attached to the condenser.