Proper humidification requires a combination of well-maintained equipment andan efficient control system that maintains the space at designed conditions underall load conditions. All humidifiers require water in one form or anotherfor humidification and most humidifier operations and maintenance problems canbe traced to water. The special problems of humidification applications haveadded a new dimension to the water treatment technology. It is the purpose ofthis discussion to review the role of humidification in today's industrial environment,humidity control systems and components, the need for system accuracy,and attendant water treatment needs.