distillation unit called a still as

distillation unit called a still as the final treatment step before storage and distribution. The high temperatures and liquid- to-vapor phase change in a still generally ensure that a distil- late will meet bacterial contamination limits. Two types of stills commonly are used: vapor compression (VC) and multi-effect (ME).A VC still may require only a softener and an activated- carbon bed as pretreatment.An ME still requires high-quality feed water. EDI commonly is used in conjunction with an ME still in pharmaceutical water treatment systems.