The aim of conducting validation is to show that the process when operated within certain limits produces the product with high degree of assurance of consistency and specified quality. To obtain water of desired quality, purity and other required specificity validation of water system is must. The validation process not only gives high quality water but it also provides a standard framework to monitor safety, efficacy and process outcome. The purpose of this discussion is an attempt to see the various aspects of validation that includes components of water treatment systems, qualification of equipment, different phases of qualification, documentation, validation, preventive maintenance, change control and post validation monitoring.